vici: Check if header has been received before processing an empty message

If do_read() returns with EWOULDBLOCK, we must ensure that we actually have
processed the full length header before checking the zero-initialized buffer
length.

src/libcharon/plugins/vici/vici_socket.c

@@ -514,7 +514,8 @@ CALLBACK(on_read, bool,
 		{
 			disconnect(this, entry->id);
 		}
-		else if (entry->in.buf.len == entry->in.done)
+		else if (entry->in.hdrlen == sizeof(entry->in.hdr) &&
+				 entry->in.buf.len == entry->in.done)
 		{
 			array_insert(entry->queue, ARRAY_TAIL, &entry->in.buf);
 			entry->in.buf = chunk_empty;