Consume data properly in Hextile decoder

We accidentally removed the code updating the data index in 8a189a6,
resulting in the decoder newer consuming any data. So the data would
be parsed as the next rect, causing weird errors.

kasmweb/core/decoders/hextile.js

@@ -129,6 +129,7 @@ export default class HextileDecoder {
                 }
                 display.finishTile();
             }
+            sock.rQi = rQi;
             this._lastsubencoding = subencoding;
             this._tiles--;
         }