avcodec/vmnc/reset_buffers(): reset cur_hx/hy too for saftey

Signed-off-by: Michael Niedermayer <michaelni@gmx.at>

libavcodec/vmnc.c

@@ -307,6 +307,8 @@ static void reset_buffers(VmncContext *c)
     av_freep(&c->curmask);
     av_freep(&c->screendta);
     c->cur_w = c->cur_h = 0;
+    c->cur_hx = c->cur_hy = 0;
+
 }
 
 static int decode_frame(AVCodecContext *avctx, void *data, int *got_frame,