Patch for new feature: show only posts with featured image

Hi David, I have seen your new release, with my credit.
Thanks.
Here is a patch I wrote to add a new feature. With this patch user can chose to show in the slider only posts with featured image. Is just one more options, and these are just a few lines. Decision is up to you.

diff -ruN ./recent-posts-flexslider-orig/recent-posts-flexslider.php ./recent-posts-flexslider/recent-posts-flexslider.php
--- ./recent-posts-flexslider-orig/recent-posts-flexslider.php	2020-01-19 13:45:14.000000000 +0100
+++ ./recent-posts-flexslider/recent-posts-flexslider.php	2020-01-20 23:06:08.519513743 +0100
@@ -92,6 +92,7 @@
 		$post_title       = $instance['post_title'];
 		$post_excerpt     = $instance['post_excerpt'];
 		$post_link        = $instance['post_link'];
+		$only_thumb_post  = $instance['only_thumb_post'];
 
 		echo $before_widget;
 
@@ -135,6 +136,7 @@
 		$instance['post_title']       = isset( $new_instance['post_title'] ) ? 'true' : 'false';
 		$instance['post_excerpt']     = isset( $new_instance['post_excerpt'] ) ? 'true' : 'false';
 		$instance['post_link']        = isset( $new_instance['post_link'] ) ? 'true' : 'false';
+		$instance['only_thumb_post']  = isset( $new_instance['only_thumb_post'] ) ? 'true' : 'false';
 
 		return $instance;
 
@@ -163,6 +165,7 @@
 			'post_excerpt'     => 'true',
 			'excerpt_length'   => 20,
 			'post_link'        => 'true',
+			'only_thumb_post'  => 'true',
 		);
 		$instance = wp_parse_args( (array) $instance, $defaults );
 
diff -ruN ./recent-posts-flexslider-orig/views/admin.php ./recent-posts-flexslider/views/admin.php
--- ./recent-posts-flexslider-orig/views/admin.php	2020-01-19 13:45:14.000000000 +0100
+++ ./recent-posts-flexslider/views/admin.php	2020-01-20 23:01:38.427302734 +0100
@@ -112,6 +112,7 @@
 				} else {
 					if ( isset( $_wp_additional_image_sizes ) && isset( $_wp_additional_image_sizes[ $s ] ) ) {
 						$sizes[ $s ] = array( $_wp_additional_image_sizes[ $s ]['width'], $_wp_additional_image_sizes[ $s ]['height'] );
+
 					}
 				}
 			}
@@ -165,4 +166,9 @@
 		<input id="<?php echo esc_attr( $this->get_field_id( 'excerpt_length' ) ); ?>" name="<?php echo esc_attr( $this->get_field_name( 'excerpt_length' ) ); ?>" value="<?php echo esc_attr( $instance['excerpt_length'] ); ?>" type="text" />
 	</div>
 
+	<div class="checkbox-wrap">
+		<input class="checkbox" type="checkbox" <?php checked( $instance['only_thumb_post'], 'true' ); ?> id="<?php echo esc_attr( $this->get_field_id( 'only_thumb_post' ) ); ?>" name="<?php echo esc_attr( $this->get_field_name( 'only_thumb_post' ) ); ?>" value="true" />
+		<label for="<?php echo esc_attr( $this->get_field_id( 'only_thumb_post' ) ); ?>"><?php esc_attr_e( 'Only posts with featured image', 'only_thumb_post' ); ?></label>
+	</div>
+	
 </div>
diff -ruN ./recent-posts-flexslider-orig/views/display.php ./recent-posts-flexslider/views/display.php
--- ./recent-posts-flexslider-orig/views/display.php	2019-02-21 14:01:22.000000000 +0100
+++ ./recent-posts-flexslider/views/display.php	2020-01-20 23:02:45.787565897 +0100
@@ -28,6 +28,10 @@
 	'ignore_sticky_posts' => true,
 );
 
+if (esc_attr( $only_thumb_post ) == 'true') {
+	$flex_args['meta_query'] = array( array ( 'key' => '_thumbnail_id', 'compare' => 'EXISTS', ));
+}
+
 $flex_query = new WP_Query( $flex_args );
 
 // Call class to display slider