Fix invalid buffer access in OOM times

Hopefully fully fixes
https://bugs.chromium.org/p/oss-fuzz/issues/detail?id=1856

src/hb-ot-layout-gsubgpos-private.hh

diff --git a/src/hb-ot-layout-gsubgpos-private.hh b/src/hb-ot-layout-gsubgpos-private.hh
index b0cffa3..dcaa261 100644
--- a/src/hb-ot-layout-gsubgpos-private.hh
+++ b/src/hb-ot-layout-gsubgpos-private.hh
@@ -1002,7 +1002,8 @@
     if (idx == 0 && lookupRecord[i].lookupListIndex == c->lookup_index)
       continue;
 
-    buffer->move_to (match_positions[idx]);
+    if (unlikely (!buffer->move_to (match_positions[idx])))
+      break;
 
     unsigned int orig_len = buffer->backtrack_len () + buffer->lookahead_len ();
     if (!c->recurse (lookupRecord[i].lookupListIndex))