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.

core/ustring.cpp

@@ -3338,7 +3338,7 @@ 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;
 				}