Normalize conversation presentation logic.

// FREEBIE

Signal/src/AppDelegate.m

@@ -555,7 +555,8 @@ static NSString *const kURLHostVerifyPrefix             = @"verify";
                                                      handler:^(UIAlertAction *_Nonnull action){
 
                                                      }]];
-        [[Environment getCurrent].homeViewController.presentedViewController presentViewController:controller
+        UIViewController *fromViewController = [[UIApplication sharedApplication] frontmostViewController];
+        [fromViewController presentViewController:controller
                                          animated:YES
                                        completion:^{
                                            completionHandler(NO);