Don't clean up update directory when Autoupdate receives SIGTERM (#2479)

Under rare circumstances, if Autoupdate receives SIGTERM while the installer queue is installing an update this could cause potential corruption.

Autoupdate/main.m

@@ -28,7 +28,11 @@ int main(int __unused argc, const char __unused *argv[])
 
         dispatch_source_t sigtermSource = dispatch_source_create(DISPATCH_SOURCE_TYPE_SIGNAL, SIGTERM, 0, dispatch_get_main_queue());
         dispatch_source_set_event_handler(sigtermSource, ^{
-            [appInstaller cleanupAndExitWithStatus:SIGTERM error:nil];
+            // Don't clear the update directory because the installer may be in middle of installing an update
+            // We still need to set an event handler for receiving SIGTERM though, otherwise our job may not terminate
+            // (This is also recommended from the developer documentation).
+            // Simply exit with SIGTERM if we recieve this signal
+            exit(SIGTERM);
         });
         dispatch_resume(sigtermSource);