fix: prevent crash when tapping marker without snippet on iOS (#568)

Author: jokerttu

ios/react-native-navigation-sdk/NavView.mm

@@ -338,7 +338,7 @@ - (void)handleMarkerInfoWindowTapped:(GMSMarker *)marker {
       marker.title != nil ? [marker.title UTF8String] : "",
       marker.opacity,
       marker.rotation,
-      [marker.snippet UTF8String],
+      marker.snippet != nil ? [marker.snippet UTF8String] : "",
       (int)marker.zIndex};
   self.eventEmitter.onMarkerInfoWindowTapped(result);
 }
@@ -350,7 +350,7 @@ - (void)handleMarkerClick:(GMSMarker *)marker {
       marker.title != nil ? [marker.title UTF8String] : "",
       marker.opacity,
       marker.rotation,
-      [marker.snippet UTF8String],
+      marker.snippet != nil ? [marker.snippet UTF8String] : "",
       (int)marker.zIndex};
   self.eventEmitter.onMarkerClick(result);
 }