Fixed _kernel_setenv.

Detail:
  _kernel_setenv(varname, NULL) should delete the variables.  It now does.
Admin:
  Tested in module.

Version 5.18. Tagged as 'RISC_OSLib-5_18'

VersionASM

@@ -9,12 +9,12 @@
                         GBLS    Module_ApplicationDate2
                         GBLS    Module_ApplicationDate4
                         GBLS    Module_HelpVersion
-Module_MajorVersion     SETS    "5.17"
-Module_Version          SETA    517
+Module_MajorVersion     SETS    "5.18"
+Module_Version          SETA    518
 Module_MinorVersion     SETS    ""
-Module_Date             SETS    "03 Oct 2000"
-Module_ApplicationDate2 SETS    "03-Oct-00"
-Module_ApplicationDate4 SETS    "03-Oct-2000"
-Module_FullVersion      SETS    "5.17"
-Module_HelpVersion      SETS    "5.17 (03 Oct 2000)"
+Module_Date             SETS    "09 Oct 2000"
+Module_ApplicationDate2 SETS    "09-Oct-00"
+Module_ApplicationDate4 SETS    "09-Oct-2000"
+Module_FullVersion      SETS    "5.18"
+Module_HelpVersion      SETS    "5.18 (09 Oct 2000)"
                         END

VersionNum

-/* (5.17)
+/* (5.18)
  *
  * This file is automatically maintained by srccommit, do not edit manually.
  *
  */
-#define Module_MajorVersion_CMHG        5.17
+#define Module_MajorVersion_CMHG        5.18
 #define Module_MinorVersion_CMHG        
-#define Module_Date_CMHG                03 Oct 2000
+#define Module_Date_CMHG                09 Oct 2000
 
-#define Module_MajorVersion             "5.17"
-#define Module_Version                  517
+#define Module_MajorVersion             "5.18"
+#define Module_Version                  518
 #define Module_MinorVersion             ""
-#define Module_Date                     "03 Oct 2000"
+#define Module_Date                     "09 Oct 2000"
 
-#define Module_ApplicationDate2         "03-Oct-00"
-#define Module_ApplicationDate4         "03-Oct-2000"
+#define Module_ApplicationDate2         "09-Oct-00"
+#define Module_ApplicationDate4         "09-Oct-2000"
 
-#define Module_FullVersion              "5.17"
-#define Module_HelpVersion              "5.17 (03 Oct 2000)"
+#define Module_FullVersion              "5.18"
+#define Module_HelpVersion              "5.18 (09 Oct 2000)"

kernel/s/k_body

@@ -2335,10 +2335,11 @@ CopyErrorString
         LoadStaticBase v6, ip
         ; Apparently, we need to say how long the value string is as well
         ; as terminating it.
-        MOV     a3, #0
-01      LDRB    ip, [a2, a3]
-        CMP     ip, #0
-        ADDNE   a3, a3, #1
+        TEQ     a2, #0
+        MOV     a3, #-1
+01      ADDNE   a3, a3, #1
+        LDRNEB  ip, [a2, a3]
+        CMPNE   ip, #0
         BNE     %B01
         MOV     r3, #0
         MOV     r4, #0