Adopt libz/libvgz fix from FreeBSD:

  r287541 | dim | 2015-09-07 20:55:14 +0000 (Mon, 07 Sep 2015) | 7 lines

  In libz's inflateMark(), avoid left-shifting a negative integer, which
  is undefined.

  Reviewed by:    delphij
  Differential Revision: https://reviews.freebsd.org/D3344
  MFC after:      3 days

lib/libvgz/inflate.c

@@ -1510,7 +1510,7 @@ z_streamp strm;
 {
     struct inflate_state FAR *state;
 
-    if (strm == Z_NULL || strm->state == Z_NULL) return -1L << 16;
+    if (strm == Z_NULL || strm->state == Z_NULL) return -(1L << 16);
     state = (struct inflate_state FAR *)strm->state;
     return ((long)(state->back) << 16) +
         (state->mode == COPY ? state->length :