CR: add some reachability asserts

SignalServiceKit/src/Util/JobQueue.swift

@@ -233,6 +233,7 @@ public extension JobQueue {
 
     func becameReachable() {
         guard requiresInternet else {
+            owsFailDebug("should only be called if `requiresInternet` is true")
             return
         }
 

SignalServiceKit/src/Util/OWSOperation.m

@@ -191,6 +191,7 @@ NSString *const OWSOperationKeyIsFinished = @"isFinished";
     self.remainingRetries--;
 
     dispatch_sync(self.retryTimerSerialQueue, ^{
+        OWSAssertDebug(self.retryTimer == nil);
         [self.retryTimer invalidate];
         self.retryTimer = [NSTimer weakScheduledTimerWithTimeInterval:self.retryInterval
                                                                target:self