[PATCH] Fix zsh goes infinite loop running completion

[Heon Jeong <blmarket@xxxxxxxxx>]

sub_match can return a negative number in a very rare condition, which
can cause zsh to hang and consume 100% cpu + ever increasing memory.

Minimal reproduction env: https://github.com/blmarket/zsh-bug

Usage: clone the repo, create docker/podman container with Dockerfile
run the container, get into /env, run ./build, run ./run, type `rm
E01` then tab tab -> hang

When the filename is utf-8 with a certain condition, its multibyte
handling can get the last 1 byte prefixed in the search string, which
is captured by the sub_match function. the caller(join_psfx) get -1 as
a result which causes the function to go into an infinite loop.

I also observed memory consumption keep increasing during the hang,
but didn't debug why.

Proposed fix is to make sure sub_match does not to return ne
gative value.

diff --git a/Src/Zle/compmatch.c b/Src/Zle/compmatch.c
index b58bd1f05..11de6ef51 100644
--- a/Src/Zle/compmatch.c
+++ b/Src/Zle/compmatch.c
@@ -2424,6 +2424,8 @@ sub_match(Cmdata md, char *str, int len, int sfx)
                md->str += l; str += l;
            }
            ret += l;
+           if (ret < 0)
+               ret = 0;
        } else if (md->line || md->len != md->olen || !md->astr)
            return ret;
        else {