reset configportal timeouts after ap disconnect

configportaltimeout now starts at configportalstart if no sta clients,
or after last client disconnects. Will never timeout if ap has sta
client! handle edge case in user code.

WiFiManager.cpp

@@ -157,6 +157,14 @@ boolean WiFiManager::autoConnect(char const *apName, char const *apPassword) {
   return startConfigPortal(apName, apPassword);
 }
 
+boolean WiFiManager::configPortalHasTimeout(){
+    if(_configPortalTimeout == 0 || wifi_softap_get_station_num() > 0){
+      _configPortalStart = millis(); // kludge, bump configportal start time to skew timeouts
+      return false;
+    }
+    return (millis() > _configPortalStart + _configPortalTimeout);
+}
+
 boolean WiFiManager::startConfigPortal() {
   String ssid = "ESP" + String(ESP.getChipId());
   return startConfigPortal(ssid.c_str(), NULL);
@@ -180,11 +188,8 @@ boolean  WiFiManager::startConfigPortal(char const *apName, char const *apPasswo
 
   while(1){
 
-    // do timeout if configPortalTimeout set and ap does not have client
-    if(_configPortalTimeout!= 0 
-        && millis() > _configPortalStart + _configPortalTimeout
-        && wifi_softap_get_station_num() == 0
-      ) break;
+    // check if timeout
+    if(configPortalHasTimeout()) break;
 
     //DNS
     dnsServer->processNextRequest();

WiFiManager.h

@@ -160,6 +160,7 @@ class WiFiManager
     void          handleNotFound();
     void          handle204();
     boolean       captivePortal();
+    boolean       configPortalHasTimeout();
 
     // DNS server
     const byte    DNS_PORT = 53;