Fix missing notifications.

// FREEBIE

Signal/src/environment/NotificationsManager.m

@@ -219,7 +219,7 @@
         // Replace any existing notification
         // e.g. when an "Incoming Call" notification gets replaced with a "Missed Call" notification.
         if (self.currentNotifications[identifier]) {
-            [self cancelNotificationWithIdentifier:identifier];
+            [self cancelNotificationWithIdentifierMainThread:identifier];
         }
 
         [[UIApplication sharedApplication] scheduleLocalNotification:notification];
@@ -232,18 +232,24 @@
 - (void)cancelNotificationWithIdentifier:(NSString *)identifier
 {
     dispatch_async(dispatch_get_main_queue(), ^{
-        UILocalNotification *notification = self.currentNotifications[identifier];
-        if (!notification) {
-            DDLogWarn(
-                @"%@ Couldn't cancel notification because none was found with identifier: %@", self.tag, identifier);
-            return;
-        }
-        [self.currentNotifications removeObjectForKey:identifier];
-
-        [[UIApplication sharedApplication] cancelLocalNotification:notification];
+        [self cancelNotificationWithIdentifierMainThread:identifier];
     });
 }
 
+- (void)cancelNotificationWithIdentifierMainThread:(NSString *)identifier
+{
+    OWSAssert([NSThread isMainThread]);
+
+    UILocalNotification *notification = self.currentNotifications[identifier];
+    if (!notification) {
+        DDLogWarn(@"%@ Couldn't cancel notification because none was found with identifier: %@", self.tag, identifier);
+        return;
+    }
+    [self.currentNotifications removeObjectForKey:identifier];
+
+    [[UIApplication sharedApplication] cancelLocalNotification:notification];
+}
+
 #pragma mark - Logging
 
 + (NSString *)tag