Kernel: Stop walking the stack when we encounter return address 0

Author: https://github.com/gunnarbeutner
Commit: 64639de4d2
Pull-request: https://github.com/SerenityOS/serenity/pull/6639
Reviewed-by: https://github.com/awesomekling

Kernel/PerformanceEventBuffer.cpp

@@ -45,6 +45,8 @@ static Vector<FlatPtr, PerformanceEvent::max_stack_frame_count> raw_backtrace(Fl
         FlatPtr retaddr;
         if (!safe_memcpy(&retaddr, (void*)(stack_ptr + sizeof(FlatPtr)), sizeof(FlatPtr), fault_at))
             break;
+        if (retaddr == 0)
+            break;
         backtrace.append(retaddr);
         if (backtrace.size() == PerformanceEvent::max_stack_frame_count)
             break;