Update LEAmDNS.cpp (issue esp8266#6982)

Check m_pUDPContext before calling functions to reset WiFi event callbacks, stop probing ... to close esp8266#6982

Author: LeisureLadi

Diff for: libraries/ESP8266mDNS/src/LEAmDNS.cpp

@@ -215,18 +215,28 @@ bool MDNSResponder::begin(const char* p_pcHostname, const IPAddress& p_IPAddress
 */
 bool MDNSResponder::close(void)
 {
+    bool    bResult = false;
 
-    m_GotIPHandler.reset();			// reset WiFi event callbacks.
-    m_DisconnectedHandler.reset();
+    if (0 != m_pUDPContext)
+    {
 
-    _announce(false, true);
-    _resetProbeStatus(false);   // Stop probing
+	  	  m_GotIPHandler.reset();			// reset WiFi event callbacks.
+  	  	m_DisconnectedHandler.reset();
 
-    _releaseServiceQueries();
-    _releaseUDPContext();
-    _releaseHostname();
+    		_announce(false, true);
+    		_resetProbeStatus(false);   // Stop probing
 
-    return true;
+    		_releaseServiceQueries();
+    		_releaseUDPContext();
+    		_releaseHostname();
+
+    		bResult = true;
+    }
+    else
+    {
+        DEBUG_EX_INFO(DEBUG_OUTPUT.printf_P(PSTR("[MDNSResponder] close: Ignoring call to close!\n")););
+    }
+	return bResult;
 }
 
 /*