MbedClient: improving logic of readSocket

Author: andreagilardoni

Diff for: libraries/SocketWrapper/src/MbedClient.cpp

@@ -19,12 +19,12 @@ void arduino::MbedClient::readSocket() {
     uint8_t data[SOCKET_BUFFER_SIZE];
     int ret = NSAPI_ERROR_WOULD_BLOCK;
     do {
-      if (rxBuffer.availableForStore() == 0) {
+      mutex->lock();
+      if (sock != nullptr && rxBuffer.availableForStore() == 0) {
+        mutex->unlock();
         yield();
         continue;
-      }
-      mutex->lock();
-      if (sock == nullptr) {
+      } else if (sock == nullptr) {
         goto cleanup;
       }
       ret = sock->recv(data, rxBuffer.availableForStore());