db-prefs: better error output for missing prefs, digest: hide DIGEST_ENABLE pref missing for unitialized users

classes/db/prefs.php

@@ -105,7 +105,7 @@ class Db_Prefs {
 			return $this->convert($value, $type_name);
 
 		} else {
-			user_error("Fatal error, unknown preferences key: $pref_name", $die_on_error ? E_USER_ERROR : E_USER_WARNING);
+			user_error("Fatal error, unknown preferences key: $pref_name (owner: $user_id)", $die_on_error ? E_USER_ERROR : E_USER_WARNING);
 			return null;
 		}
 	}

include/digest.php

@@ -26,7 +26,7 @@
 
 		while ($line = db_fetch_assoc($result)) {
 
-			if (get_pref('DIGEST_ENABLE', $line['id'], false)) {
+			if (@get_pref('DIGEST_ENABLE', $line['id'], false)) {
 				$preferred_ts = strtotime(get_pref('DIGEST_PREFERRED_TIME', $line['id'], '00:00'));
 
 				// try to send digests within 2 hours of preferred time