[ios] Fix points/shapes typo that caused crash (#5142)

#5097 introduced different arrays for points and shapes, but only ever attempted to use the points array. Adding a shape would crash.

platform/ios/src/MGLMapView.mm

@@ -2902,7 +2902,7 @@ - (void)addAnnotations:(NS_ARRAY_OF(id <MGLAnnotation>) *)annotations
         for (size_t i = 0; i < annotationTags.size(); ++i)
         {
             MGLAnnotationTag annotationTag = annotationTags[i];
-            id <MGLAnnotation> annotation = userPoints[i];
+            id <MGLAnnotation> annotation = userShapes[i];
 
             MGLAnnotationContext context;
             context.annotation = annotation;