SARA R410 also "forget" to notify about incoming data

src/TinyGsmClientSIM800.h

@@ -100,6 +100,7 @@ public:
     // closes until all data is read from the buffer.
     // Doing it this way allows the external mcu to find and get all of the data
     // that it wants from the socket even if it was closed externally.
+    rx.clear();
     at->maintain();
     while (sock_available > 0) {
       sock_available -= at->modemRead(TinyGsmMin((uint16_t)rx.free(), sock_available), mux);
@@ -153,7 +154,6 @@ public:
         cnt += chunk;
         continue;
       }
-      // TODO: Read directly into user buffer?
       // Workaround: sometimes SIM800 forgets to notify about data arrival.
       // TODO: Currently we ping the module periodically,
       // but maybe there's a better indicator that we need to poll
@@ -162,6 +162,7 @@ public:
         prev_check = millis();
       }
       at->maintain();
+      // TODO: Read directly into user buffer?
       if (sock_available > 0) {
         sock_available -= at->modemRead(TinyGsmMin((uint16_t)rx.free(), sock_available), mux);
       } else {