[ios] Avoid removing annotations from torn-down map

If the underlying mbgl::Map has been torn down, so has the mbgl annotation, so don’t worry about the mbgl::Map but keep unregistering KVO and other SDK-side annotation resources.

platform/ios/CHANGELOG.md

@@ -30,6 +30,7 @@ Mapbox welcomes participation and contributions from everyone. Please read [CONT
 ### Other changes
 
 * Added the `MGLMapView.minimumPitch` and `MGLMapView.maximumPitch` properties to further limit how much the user or your code can tilt the map. ([#208](https://github.com/mapbox/mapbox-gl-native-ios/pull/208))
+* Fixed a crash while quitting the application after adding an annotation to `MGLMapView`. ([#252](https://github.com/mapbox/mapbox-gl-native-ios/pull/252))
 * Improved performance when continuously animating a tilted map. ([#16287](https://github.com/mapbox/mapbox-gl-native/pull/16287))
 * Fixed a memory leak when zooming with any options enabled in the `MGLMapView.debugMask` property. ([#15179](https://github.com/mapbox/mapbox-gl-native/issues/15179))
 

platform/ios/src/MGLMapView.mm

@@ -4612,7 +4612,12 @@ public:
         }
 
         _isChangingAnnotationLayers = YES;
-        self.mbglMap.removeAnnotation(annotationTag);
+        // If the underlying map is gone, there’s nothing to remove, but still
+        // continue to unregister KVO and other annotation resources.
+        if (_mbglMap)
+        {
+            self.mbglMap.removeAnnotation(annotationTag);
+        }
     }
 
     [self updatePresentsWithTransaction];