iOS: guard image picker logic to check for the right source type

Summary:
The logic in the method is only relevant if the sourceType is `UIImagePickerControllerSourceTypeCamera`. So we guard it here, to prevent NSInvalidArgumentException.

Changelog: [Internal]

Reviewed By: sammy-SC

Differential Revision: D19184818

fbshipit-source-id: 5c99dabfaed23629e22fdc888263bd09e8768c88

Libraries/CameraRoll/RCTImagePickerManager.mm

@@ -236,6 +236,9 @@ - (void)_dismissPicker:(UIImagePickerController *)picker args:(NSArray *)args
 - (void)cameraChanged:(NSNotification *)notification
 {
   for (UIImagePickerController *picker in _pickers) {
+    if (picker.sourceType != UIImagePickerControllerSourceTypeCamera) {
+      continue;
+    }
     if ([picker isKindOfClass:[RCTImagePickerController class]]
       && ((RCTImagePickerController *)picker).unmirrorFrontFacingCamera
       && picker.cameraDevice == UIImagePickerControllerCameraDeviceFront) {