[morx] Leave ligature on stack after ligating

Test with Apple Color Emoji.ttf of ~66MB and following sequence:

./hb-shape Apple\ Color\ Emoji-old.ttf --font-funcs=ot -u U+1F468,200d,U+1F469,200d,U+1F467,200d,1f466

Should form full family if matching works correctly.  It first makes
family of three, then makes family of four out of that and the last
two characters.

Fixes https://github.com/harfbuzz/harfbuzz/issues/1292

diff --git a/src/hb-aat-layout-morx-table.hh b/src/hb-aat-layout-morx-table.hh
index 651af21..ddb444c 100644 (file)
--- a/src/hb-aat-layout-morx-table.hh
+++ b/src/hb-aat-layout-morx-table.hh
@@ -442,7 +442,6 @@ struct LigatureSubtable
          action_idx++;
        }
        while (!(action & LigActionLast));
-       match_length = 0;
        buffer->move_to (end);
       }