unposted: change '\0' to NULL to silence spurious compile warning.

params.c:830:13: warning: expression which evaluates to zero treated as a null
      pointer constant of type 'char *' [-Wnon-literal-null-conversion]
    *envp = '\0';

Src/params.c

@@ -827,7 +827,7 @@ createparamtable(void)
     }
     popheap();
 #ifndef USE_SET_UNSET_ENV
-    *envp = '\0';
+    *envp = NULL;
 #endif
     opts[ALLEXPORT] = oae;