Make sure that array key exists

Author: Marco Pereirinha

php/class-media.php

@@ -1718,7 +1718,7 @@ public function get_breakpoint_options( $attachment_id ) {
 		$breakpoints = array();
 		$settings    = $this->settings->get_setting( self::MEDIA_SETTINGS_SLUG )->get_value();
 
-		if ( $settings['enable_breakpoints'] && wp_attachment_is_image( $attachment_id ) ) {
+		if ( ! empty( $settings['enable_breakpoints'] ) && wp_attachment_is_image( $attachment_id ) ) {
 			$meta = wp_get_attachment_metadata( $attachment_id );
 			// Get meta image size if non exists.
 			if ( empty( $meta ) ) {