ralloc: Use strnlen() inside of strncat()

If the str is long or isn't null-terminated, strlen() could take a lot
of time or even crash. I don't know why was it used in the first place,
maybe for platforms without strnlen(), but strnlen() is already used
inside of ralloc_strndup(), so this change should not additionally
break anything.

Reviewed-by: Ian Romanick <ian.d.romanick@intel.com>
Reviewed-by: Timothy Arceri <tarceri@itsqueeze.com>

src/util/ralloc.c

@@ -405,12 +405,7 @@ ralloc_strcat(char **dest, const char *str)
 bool
 ralloc_strncat(char **dest, const char *str, size_t n)
 {
-   /* Clamp n to the string length */
+   return cat(dest, str, strnlen(str, n));
-   size_t str_length = strlen(str);
-   if (str_length < n)
-      n = str_length;
-
-   return cat(dest, str, n);
 }
 
 char *