Issue #407: fix incorrect casts in calls to ctype functions (isdigit and isspace) so we don't crash when asserts are enabled on certain platforms and characters > 128 are parsed.

json_object.c

@@ -838,7 +838,7 @@ static int json_object_double_to_json_string_format(struct json_object* jso,
 			format_drops_decimals = 1;
 
 		if (size < (int)sizeof(buf) - 2 &&
-		    isdigit((int)buf[0]) && /* Looks like *some* kind of number */
+		    isdigit((unsigned char)buf[0]) && /* Looks like *some* kind of number */
 			!p && /* Has no decimal point */
 		    strchr(buf, 'e') == NULL && /* Not scientific notation */
 			format_drops_decimals)

json_pointer.c

@@ -44,7 +44,7 @@ static int is_valid_index(struct json_object *jo, const char *path, int32_t *idx
 	/* this code-path optimizes a bit, for when we reference the 0-9 index range in a JSON array
 	   and because leading zeros not allowed */
 	if (len == 1) {
-		if (isdigit((int)path[0])) {
+		if (isdigit((unsigned char)path[0])) {
 			*idx = (path[0] - '0');
 			goto check_oob;
 		}
@@ -58,7 +58,7 @@ static int is_valid_index(struct json_object *jo, const char *path, int32_t *idx
 	}
 	/* RFC states base-10 decimals */
 	for (i = 0; i < len; i++) {
-		if (!isdigit((int)path[i])) {
+		if (!isdigit((unsigned char)path[i])) {
 			errno = EINVAL;
 			return 0;
 		}

json_tokener.c

@@ -295,7 +295,7 @@ struct json_object* json_tokener_parse_ex(struct json_tokener *tok,
 
     case json_tokener_state_eatws:
       /* Advance until we change state */
-      while (isspace((int)c)) {
+      while (isspace((unsigned char)c)) {
 	if ((!ADVANCE_CHAR(str, tok)) || (!PEEK_CHAR(c, tok)))
 	  goto out;
       }