Fix PHP7 warning "session_start(): Session callback expects true/false return value" (#1490624)

CHANGELOG

@@ -9,6 +9,7 @@ CHANGELOG Roundcube Webmail
 - Fix so drag-n-drop of text (e.g. recipient addresses) on compose page actually works (#1490619)
 - Fix .htaccess rewrite rules to not block .well-known URIs (#1490615)
 - Fix mail view scaling on iOS (#1490551)
+- Fix PHP7 warning "session_start(): Session callback expects true/false return value" (#1490624)
 
 RELEASE 1.2-beta
 ----------------

program/lib/Roundcube/rcube_session.php

@@ -219,7 +219,9 @@ abstract class rcube_session
     {
         // move gc execution to the script shutdown function
         // see rcube::shutdown() and rcube_session::write_close()
-        return $this->gc_enabled = $maxlifetime;
+        $this->gc_enabled = $maxlifetime;
+
+        return true;
     }
 
     /**