fix(videos): videos not working on iOS 13 and throwing a fatal crash …

…when selected (#1904)

* Fix GH-1742: Additional error check for nil around copying video and adds error message handling to prevent hard crash.
* Fix GH-1742: Lower case "nil" in conditional check

ios/ImagePickerManager.m

@@ -197,7 +197,7 @@ -(NSMutableDictionary *)mapVideoToAsset:(NSURL *)url phAsset:(PHAsset * _Nullabl
             [fileManager copyItemAtURL:url toURL:videoDestinationURL error:error];
           }
 
-          if (error) {
+          if (error && *error) {
               return nil;
           }
         }
@@ -352,8 +352,11 @@ - (void)imagePickerController:(UIImagePickerController *)picker didFinishPicking
         } else {
             NSError *error;
             NSDictionary *videoAsset = [self mapVideoToAsset:info[UIImagePickerControllerMediaURL] phAsset:asset error:&error];
+
             if (videoAsset == nil) {
-                self.callback(@[@{@"errorCode": errOthers, @"errorMessage":  error.localizedFailureReason}]);
+                NSString *errorMessage = error.localizedFailureReason;
+                if (errorMessage == nil) errorMessage = @"Video asset not found";
+                self.callback(@[@{@"errorCode": errOthers, @"errorMessage": errorMessage}]);
                 return;
             }
             [assets addObject:videoAsset];