Add NULL-terminator the string passed to strtol.

This is actually expected by the function although it was apparently
working in GCC without the terminator, it breaks (at least some) clang
versions.

(cherry picked from commit 2f91e250f601e61e58fcb63b9bd72d29d7fc866b)

core/ustring.cpp

@@ -3297,7 +3297,7 @@ String String::http_unescape() const {
 			if ((ord1 >= '0' && ord1 <= '9') || (ord1 >= 'A' && ord1 <= 'Z')) {
 				CharType ord2 = ord_at(i + 2);
 				if ((ord2 >= '0' && ord2 <= '9') || (ord2 >= 'A' && ord2 <= 'Z')) {
-					char bytes[2] = { (char)ord1, (char)ord2 };
+					char bytes[3] = { (char)ord1, (char)ord2, 0 };
 					res += (char)strtol(bytes, NULL, 16);
 					i += 2;
 				}