Handle MQTT host string with port omitted

src/mqtt/MQTT.cpp

@@ -69,10 +69,14 @@ void MQTT::reconnect()
 
     String server = String(serverAddr);  
     int delimIndex = server.indexOf(':'); 
-    String host = server.substring(0, delimIndex);
-    String port = server.substring(delimIndex+1, server.length());
-
-    pubSub.setServer(host.c_str(), port.toInt());
+    if (delimIndex > 0) {
+        String host = server.substring(0, delimIndex);
+        String port = server.substring(delimIndex+1, server.length());
+        pubSub.setServer(host.c_str(), port.toInt());
+    }
+    else {
+        pubSub.setServer(serverAddr, 1883);
+    }
 
     DEBUG_MSG("Connecting to MQTT server\n", serverAddr);
     auto myStatus = (statusTopic + owner.id);