[zlib] Avoid wide writes to dst in crc_fold_copy when len < 16

When copying directly to next_out, as is done in deflate_stored, there
may not be enough space in the buffer.

Fix by jmaaninen, test by me.

Bug: 325990053
Change-Id: Ia28d3fac9c2db3f27a23a5fbde399cad323ef40d
Reviewed-on: https://chromium-review.googlesource.com/c/chromium/src/+/5307227


Commit-Queue: Adenilson Cavalcanti <cavalcantii@chromium.org>
Reviewed-by: Adenilson Cavalcanti <cavalcantii@chromium.org>
Cr-Commit-Position: refs/heads/main@{#1263750}
NOKEYCHECK=True
GitOrigin-RevId: 67c52873de10c06808c0de985a1e3cb8c3456d7a