Add null hash table entry checks to SysCommsModule & UtilityModule hash table lookup

Detail:
  s/Oscli - In SysCommsHashedLookup and UtilCommsHashedLookup, check for null hash table entries instead of just blindly calling ModCommsLookUp_AltEntry.
  This fixes an issue where a crash will occur iff:
  (a) You enter a command which has no entry in one of the two hash tables
  (b) The command is a valid command (with a code entry point) if you reinterpret the corresponding module header as a command table
  In reality, for recent versions of RISC OS 5, you'll get a crash only when trying to execute the command 's'. Some previous OS versions (e.g. 5.12) appear to have been immune to the crash.
  If (a) was true but (b) was false the bug would have also resulted in a small performance hit caused by attempting to scan the module headers for matching commands.
Admin:
  Tested in Tungsten & OMAP ROM builds
  's' no longer crashes, and commands included in the two hash tables still seem to function as normal.
  Fixes issue reported on forums:
  http://www.riscosopen.org/forum/forums/4/topics/902


Version 5.35, 4.79.2.135. Tagged as 'Kernel-5_35-4_79_2_135'

VersionASM

@@ -13,11 +13,11 @@
                         GBLS    Module_ComponentPath
 Module_MajorVersion     SETS    "5.35"
 Module_Version          SETA    535
-Module_MinorVersion     SETS    "4.79.2.134"
-Module_Date             SETS    "27 Jan 2012"
-Module_ApplicationDate  SETS    "27-Jan-12"
+Module_MinorVersion     SETS    "4.79.2.135"
+Module_Date             SETS    "31 Jan 2012"
+Module_ApplicationDate  SETS    "31-Jan-12"
 Module_ComponentName    SETS    "Kernel"
 Module_ComponentPath    SETS    "castle/RiscOS/Sources/Kernel"
-Module_FullVersion      SETS    "5.35 (4.79.2.134)"
-Module_HelpVersion      SETS    "5.35 (27 Jan 2012) 4.79.2.134"
+Module_FullVersion      SETS    "5.35 (4.79.2.135)"
+Module_HelpVersion      SETS    "5.35 (31 Jan 2012) 4.79.2.135"
                         END

VersionNum

@@ -5,19 +5,19 @@
  *
  */
 #define Module_MajorVersion_CMHG        5.35
-#define Module_MinorVersion_CMHG        4.79.2.134
-#define Module_Date_CMHG                27 Jan 2012
+#define Module_MinorVersion_CMHG        4.79.2.135
+#define Module_Date_CMHG                31 Jan 2012
 
 #define Module_MajorVersion             "5.35"
 #define Module_Version                  535
-#define Module_MinorVersion             "4.79.2.134"
-#define Module_Date                     "27 Jan 2012"
+#define Module_MinorVersion             "4.79.2.135"
+#define Module_Date                     "31 Jan 2012"
 
-#define Module_ApplicationDate          "27-Jan-12"
+#define Module_ApplicationDate          "31-Jan-12"
 
 #define Module_ComponentName            "Kernel"
 #define Module_ComponentPath            "castle/RiscOS/Sources/Kernel"
 
-#define Module_FullVersion              "5.35 (4.79.2.134)"
-#define Module_HelpVersion              "5.35 (27 Jan 2012) 4.79.2.134"
+#define Module_FullVersion              "5.35 (4.79.2.135)"
+#define Module_HelpVersion              "5.35 (31 Jan 2012) 4.79.2.135"
 #define Module_LibraryVersionInfo       "5:35"

s/Oscli

@@ -815,12 +815,13 @@ schl_nofudgesofar
          CMP    R4, #4
          BLS    schl_fudgeloop
 schl_nofudge
-         AND    R4, R1,#Oscli_CHashValMask  ;hash value, masked for command hashing
-         ADRL   R1, SysCommsModule
          ADRL   R2, SysCoHashedCmdTab
+         AND    R4, R1,#Oscli_CHashValMask  ;hash value, masked for command hashing
          LDR    R2, [R2, R4, LSL #2]        ;command list for this hash value
-         SEC                                ;carry set means sys module
-         B      ModCommsLookUp_AltEntry
+         ADRL   R1, SysCommsModule
+         CMP    R2, #1                      ;set carry if valid table entry
+         BCS    ModCommsLookUp_AltEntry     ;note: carry set to indicate sys module
+         Pull   "R0, R2-R10, pc"            ;bail if null hash table entry (with carry clear to indicate failure)
 schl_fudge
          ADRL   R1, SysCommsModule
          ADRL   R2, SHC_fudgeulike
@@ -835,12 +836,13 @@ schl_fudge
 
 UtilCommsHashedLookup ROUT
          Push   "R0, R2-R10, lr"
-         AND    R4, R1,#Oscli_CHashValMask  ;hash value, masked for command hashing
-         ADRL   R1, UtilityMod
          ADRL   R2, UtilHashedCmdTab
+         AND    R4, R1,#Oscli_CHashValMask  ;hash value, masked for command hashing
          LDR    R2, [R2, R4, LSL #2]        ;command list for this hash value
-         CLC
-         B      ModCommsLookUp_AltEntry
+         ADRL   R1, UtilityMod
+         TEQ    R2, #0,2                    ;check R2 and clear carry
+         BNE    ModCommsLookUp_AltEntry
+         Pull   "R0, R2-R10, pc"            ;bail if null hash table entry
 ;
   ] ;Oscli_HashedCommands