Move app state check to main thread.

SignalServiceKit/src/Messages/OWSDisappearingMessagesJob.m

@@ -363,11 +363,12 @@ void AssertIsOnDisappearingMessagesQueue()
         recentlyScheduledDisappearanceTimer = YES;
     }
 
-    dispatch_async(OWSDisappearingMessagesJob.serialQueue, ^{
     if (!CurrentAppContext().isMainAppAndActive) {
         DDLogInfo(@"%@ Ignoring fallbacktimer for app which is not main and active.", self.logTag);
         return;
     }
+
+    dispatch_async(OWSDisappearingMessagesJob.serialQueue, ^{
         NSUInteger deletedCount = [self runLoop];
 
         // Normally deletions should happen via the disappearanceTimer, to make sure that they're prompt.