Ensure application data records are not kept when fully processed

This commit fixes the following case: If a client is both expecting a
SERVER_HELLO and has an application data record that's partially
processed in flight (that's the situation the client gets into after
receiving a ServerHelloRequest followed by ApplicationData), a
subsequent call to mbedtls_ssl_read will set keep_current_message = 1
when seeing the unexpected application data, but not reset it to 0
after the application data has been processed. This commit fixes this.
diff --git a/library/ssl_tls.c b/library/ssl_tls.c
index dafef1f..bd2c270 100644
--- a/library/ssl_tls.c
+++ b/library/ssl_tls.c
@@ -6780,8 +6780,11 @@
     ssl->in_msglen -= n;
 
     if( ssl->in_msglen == 0 )
+    {
         /* all bytes consumed  */
         ssl->in_offt = NULL;
+        ssl->keep_current_message = 0;
+    }
     else
         /* more data available */
         ssl->in_offt += n;