Fixed some data aborts on OS_Args calls

Detail:
  OS_Args 8 and 9 (ImageStampIS and IOCtl) didn't check that the file handle
passed to them was legitimate and hence would cause data aborts as they tried
to access non existant structures.

Admin:
  Not tested.  Two lines of assembler copied into each function to test
whether the file handle is valid from other similar calls.

Version 2.56. Tagged as 'FileSwitch-2_56'

VersionASM

@@ -11,14 +11,14 @@
                         GBLS    Module_HelpVersion
                         GBLS    Module_ComponentName
                         GBLS    Module_ComponentPath
-Module_MajorVersion     SETS    "2.55"
-Module_Version          SETA    255
+Module_MajorVersion     SETS    "2.56"
+Module_Version          SETA    256
 Module_MinorVersion     SETS    ""
-Module_Date             SETS    "03 Apr 2001"
-Module_ApplicationDate2 SETS    "03-Apr-01"
-Module_ApplicationDate4 SETS    "03-Apr-2001"
+Module_Date             SETS    "04 Apr 2001"
+Module_ApplicationDate2 SETS    "04-Apr-01"
+Module_ApplicationDate4 SETS    "04-Apr-2001"
 Module_ComponentName    SETS    "FileSwitch"
 Module_ComponentPath    SETS    "RiscOS/Sources/FileSys/FileSwitch"
-Module_FullVersion      SETS    "2.55"
-Module_HelpVersion      SETS    "2.55 (03 Apr 2001)"
+Module_FullVersion      SETS    "2.56"
+Module_HelpVersion      SETS    "2.56 (04 Apr 2001)"
                         END

VersionNum

-/* (2.55)
+/* (2.56)
  *
  * This file is automatically maintained by srccommit, do not edit manually.
  *
  */
-#define Module_MajorVersion_CMHG        2.55
+#define Module_MajorVersion_CMHG        2.56
 #define Module_MinorVersion_CMHG        
-#define Module_Date_CMHG                03 Apr 2001
+#define Module_Date_CMHG                04 Apr 2001
 
-#define Module_MajorVersion             "2.55"
-#define Module_Version                  255
+#define Module_MajorVersion             "2.56"
+#define Module_Version                  256
 #define Module_MinorVersion             ""
-#define Module_Date                     "03 Apr 2001"
+#define Module_Date                     "04 Apr 2001"
 
-#define Module_ApplicationDate2         "03-Apr-01"
-#define Module_ApplicationDate4         "03-Apr-2001"
+#define Module_ApplicationDate2         "04-Apr-01"
+#define Module_ApplicationDate4         "04-Apr-2001"
 
 #define Module_ComponentName            "FileSwitch"
 #define Module_ComponentPath            "RiscOS/Sources/FileSys/FileSwitch"
 
-#define Module_FullVersion              "2.55"
-#define Module_HelpVersion              "2.55 (03 Apr 2001)"
+#define Module_FullVersion              "2.56"
+#define Module_HelpVersion              "2.56 (04 Apr 2001)"

s/OSArgs

@@ -175,6 +175,8 @@ FileArgs_ReadPath
         B       FileArgsExit
 
 FileArgs_IOCtl
+        TST     status, #scb_unallocated
+        BNE     %FA92
 	Push	"r0-r1, fscb"
         LDR     fscb, scb_fscb
 	LDR	r0, [fscb, #fscb_extra]
@@ -191,6 +193,8 @@ FileArgs_ImageStampIs
         DREG    r1, "ImageStampIs on file ",cc
         DREG    r2, " is "
  ]
+        TST     status, #scb_unallocated
+        BNE     %FA92
         LDR     r0, scb_fscb
         LDR     r0, [r0, #fscb_info]
         TST     r0, #fsinfo_multifsextensions