Fix crash when trying to remove popped view controller that doesn't exist

Tusker/Screens/Utilities/EnhancedNavigationViewController.swift

@@ -141,13 +141,15 @@ class EnhancedNavigationViewController: UINavigationController {
                 if self.interactivePushTransition.interactive {
                     // when an interactive push gesture is cancelled, make sure to adding the VC that was being pushed back onto the popped stack so it doesn't disappear
                     self.poppedViewControllers.insert(self.interactivePushTransition.pushingViewController!, at: 0)
-                } else {
+                } else if self.interactivePopGestureRecognizer?.state == .ended {
                     // when an interactive pop gesture is cancelled (i.e. the user lifts their finger before it triggers),
                     // the popViewController(animated:) method has already been called so the VC has already been added to the popped stack
                     // so we make sure to remove it, otherwise there could be duplicate VCs on the navigation stasck
+                    if !self.poppedViewControllers.isEmpty {
                         self.poppedViewControllers.remove(at: 0)
                     }
                 }
+            }
         })
     }