jim.c: Use UCHAR() with isxxx() functions

For systems with signed char

Signed-off-by: Steve Bennett <steveb@workware.net.au>

1 files changed, 1 insertions, 1 deletions

diff --git a/jim.c b/jim.c
index 65b434e..3c52f74 100644
--- a/jim.c
+++ b/jim.c
@@ -3032,7 +3032,7 @@ static int JimStringIs(Jim_Interp *interp, Jim_Obj *strObjPtr, Jim_Obj *strClass
     }
 
     for (i = 0; i < len; i++) {
-        if (!isclassfunc(str[i])) {
+        if (!isclassfunc(UCHAR(str[i]))) {
             Jim_SetResultBool(interp, 0);
             return JIM_OK;
         }