Fix some warnings and wrap ESP8266 Client overrides in #ifdef (#22)

Author: sandeepmistry

src/MqttClient.h

@@ -67,7 +67,9 @@ class MqttClient : public Client {
   // from Client
   virtual int connect(IPAddress ip, uint16_t port = 1883);
   virtual int connect(const char *host, uint16_t port = 1883);
-  virtual int connect(const IPAddress& ip, uint16_t port) { }; /* ESP8266 core defines this pure virtual in Client.h */
+#ifdef ESP8266
+  virtual int connect(const IPAddress& ip, uint16_t port) { return connect(ip, port); }; /* ESP8266 core defines this pure virtual in Client.h */
+#endif
   virtual size_t write(uint8_t);
   virtual size_t write(const uint8_t *buf, size_t size);
   virtual int available();
@@ -92,9 +94,10 @@ class MqttClient : public Client {
 
   int connectError() const;
   int subscribeQoS() const;
-  virtual bool flush(unsigned int maxWaitMs) { } /* ESP8266 core defines this pure virtual in Client.h */
-
-  virtual bool stop(unsigned int maxWaitMs)  { } /* ESP8266 core defines this pure virtual in Client.h */
+#ifdef ESP8266
+  virtual bool flush(unsigned int /*maxWaitMs*/) { flush(); return true; } /* ESP8266 core defines this pure virtual in Client.h */
+  virtual bool stop(unsigned int /*maxWaitMs*/)  { stop(); return true; } /* ESP8266 core defines this pure virtual in Client.h */
+#endif
 
 private:
   int connect(IPAddress ip, const char* host, uint16_t port);