Fix memory leak when incompressable

Don't leak longs and shorts when skipping compression.
Found by cppcheck static analysis.

Version 5.17. Tagged as 'squeeze-5_17'

VersionNum

-/* (5.16)
+/* (5.17)
  *
  * This file is automatically maintained by srccommit, do not edit manually.
  * Last processed by srccommit version: 1.1.
  *
  */
-#define Module_MajorVersion_CMHG        5.16
+#define Module_MajorVersion_CMHG        5.17
 #define Module_MinorVersion_CMHG        
-#define Module_Date_CMHG                08 May 2015
+#define Module_Date_CMHG                19 Aug 2018
 
-#define Module_MajorVersion             "5.16"
-#define Module_Version                  516
+#define Module_MajorVersion             "5.17"
+#define Module_Version                  517
 #define Module_MinorVersion             ""
-#define Module_Date                     "08 May 2015"
+#define Module_Date                     "19 Aug 2018"
 
-#define Module_ApplicationDate          "08-May-15"
+#define Module_ApplicationDate          "19-Aug-18"
 
 #define Module_ComponentName            "squeeze"
 #define Module_ComponentPath            "castle/RiscOS/Tools/Sources/squeeze"
 
-#define Module_FullVersion              "5.16"
-#define Module_HelpVersion              "5.16 (08 May 2015)"
-#define Module_LibraryVersionInfo       "5:16"
+#define Module_FullVersion              "5.17"
+#define Module_HelpVersion              "5.17 (19 Aug 2018)"
+#define Module_LibraryVersionInfo       "5:17"

c/squeeze

@@ -263,7 +263,7 @@ static char *heaplwm;
 static char *heaphwm;
 #endif
 
-static void *xalloc(int bytes, char *what)
+static void *xalloc(int bytes, const char *what)
 { void *p = malloc(bytes);
   if (p == NULL) err_fail("no more room");
 /*  if ((int)p < 0) err_fail("storage corruption (%d)", (int)p); */
@@ -700,7 +700,11 @@ static char *compresscode(word *code, int size, int execoffset)
 	  (nliterals	 * 100) / nwords);
 
   if (guess > (9*size)/10) { /* not much squeeze to be had */
-    if ((!force) || (guess > size)) return(NULL);
+    if ((!force) || (guess > size)) {
+      xfree(shorts);
+      xfree(longs);
+      return(NULL);
+    }
   }
 
   /*