Clear segment counter at beginning

This fixes an encoder/decoder mismatch for aq-mode when configure with
--enable-misc-fixes.

BUG=https://bugs.chromium.org/p/aomedia/issues/detail?id=24

Change-Id: I96d77d6556930837adf8f3f21cfa4d80f2ddfd15

av1/encoder/segmentation.c

@@ -233,6 +233,7 @@ void av1_choose_segmap_coding_method(AV1_COMMON *cm, MACROBLOCKD *xd) {
 
 #if CONFIG_MISC_FIXES
   (void)xd;
+  av1_zero(cm->counts.seg);
 #else
   // Set default state for the segment tree probabilities and the
   // temporal coding probabilities