hotfix for issue with the potential to stuff up the queuewrker

(cherry picked from commit 794b456b8a)

Co-authored-by: Mario Vavti <mario@mariovavti.com>

Zotlabs/Lib/Activity.php

@@ -3334,6 +3334,12 @@ class Activity {
 			return true;
 		}
 
+		// FIXME: it appears sometimes $s is an array (needs invetigation)
+		if (!is_string($s)) {
+			btlogger('Not a string: ' . print_r($s, true));
+			return true;
+		}
+
 		$s_alt = htmlspecialchars($s, ENT_QUOTES, 'UTF-8');
 
 		if (