initialize ptr to nullptr in handle_out_of_memory

It will break out of the loop in the first iteration if there's no
handler or the handler throws an out-of-memory error.

new.cc

@@ -9,7 +9,7 @@ extern "C" {
 }
 
 COLD static void *handle_out_of_memory(size_t size, bool nothrow) {
-    void *ptr;
+    void *ptr = nullptr;
 
     do {
         std::new_handler handler = std::get_new_handler();