Clear buffer on stop(). Fix #119

src/TinyGsmClientSIM800.h

@@ -72,6 +72,7 @@ public:
 
 public:
   virtual int connect(const char *host, uint16_t port) {
+    stop();
     TINY_GSM_YIELD();
     rx.clear();
     sock_connected = at->modemConnect(host, port, mux);
@@ -95,6 +96,7 @@ public:
     at->sendAT(GF("+CIPCLOSE="), mux);
     sock_connected = false;
     at->waitResponse();
+    rx.clear();
   }
 
   virtual size_t write(const uint8_t *buf, size_t size) {
@@ -191,6 +193,7 @@ public:
 
 public:
   virtual int connect(const char *host, uint16_t port) {
+    stop();
     TINY_GSM_YIELD();
     rx.clear();
     sock_connected = at->modemConnect(host, port, mux, true);