Add a safeguard for Sharing post filter results.

projects/plugins/jetpack/changelog/add-sharing-safeguard-post

@@ -0,0 +1,4 @@
+Significance: patch
+Type: bugfix
+
+Sharing: Fix possible warnings related to plugin compatibility.

projects/plugins/jetpack/modules/sharedaddy/sharing-service.php

@@ -960,7 +960,12 @@
 		return $text;
 	}
 
+	// We require the post to not be empty and be an actual WordPress post object. If it's not - we just return.
+	if ( empty( $post ) || ! $post instanceof \WP_Post ) {
+		return $text;
+	}
+
 	if ( empty( $post ) ) {
 		return $text;
 	}