ref(xmpp): capture error msg from Strophe ERROR state

If Strophe goes to the ERROR state it will pass the error message there
and then transition to the DISCONNECTED state, but without any error
msg.

modules/xmpp/xmpp.js

@@ -215,6 +215,8 @@ export default class XMPP extends Listenable {
 
             logger.info(`My Jabber ID: ${this.connection.jid}`);
 
+            this.lastErrorMsg = undefined;
+
             // Schedule ping ?
             const pingJid = this.connection.domain;
 
@@ -277,6 +279,8 @@ export default class XMPP extends Listenable {
                     JitsiConnectionEvents.CONNECTION_FAILED,
                     JitsiConnectionErrors.OTHER_ERROR, msg);
             }
+        } else if (status === Strophe.Status.ERROR) {
+            this.lastErrorMsg = msg;
         } else if (status === Strophe.Status.DISCONNECTED) {
             // Stop ping interval
             this.connection.ping.stopInterval();