internal.c: check that we have data before processing messages

We should never encounter this bug under normal circumstances. But if we enter
processReplyEx with a wrongly `ssl->options.processReply` set to
`runProcessingOneMessage` we check that we have some data.

src/internal.c

@@ -17396,6 +17396,10 @@ int ProcessReplyEx(WOLFSSL* ssl, int allowSocketErr)
 
         /* the record layer is here */
         case runProcessingOneMessage:
+            /* can't process a message if we have no data.  */
+            if (ssl->buffers.inputBuffer.idx
+                >= ssl->buffers.inputBuffer.length)
+                return BUFFER_ERROR;
 
        #if defined(HAVE_ENCRYPT_THEN_MAC) && !defined(WOLFSSL_AEAD_ONLY)
             if (IsEncryptionOn(ssl, 0) && ssl->options.startedETMRead) {