Avoid typecasting a signed char to an int when using is*() functions, as that

could very well cause a negate number get passed in and thus cause reading
outside of the array usually used for this purpose.

We avoid this by using the uppercase macro versions introduced just now that
does some extra crazy typecasts to avoid byte codes > 127 to cause negative
int values.

lib/mprintf.c

@@ -171,7 +171,7 @@ int curl_msprintf(char *buffer, const char *format, ...);
 static long dprintf_DollarString(char *input, char **end)
 {
   int number=0;
-  while(isdigit((int)*input)) {
+  while(ISDIGIT(*input)) {
     number *= 10;
     number += *input-'0';
     input++;