kernel: Avoid processing unregistered signals for init

kernel/src/thread/Thread.cpp

@@ -117,6 +117,12 @@ void Thread::process_pending_signals(Registers* current_regs)
             if (handler.sa_handler == SIG_DFL)
             {
             default_signal:
+                if (id == 1)
+                {
+                    kwarnln("signal: init got a signal it has no handler for, ignoring");
+                    return;
+                }
+
                 kinfoln("signal: using default behavior (handler=SIG_DFL) (terminating)");
                 // FIXME: Add different default handlers for different signals and add signal exit codes.
                 exit_and_signal_parent(255);