fix: Use of uninitialized value

The subroutine did not check the case where HEAD does not verify.

Patch from Junio C Hamano <junkio@cox.net>

diff --git a/gitweb.cgi b/gitweb.cgi
index 986d7da..cb03373 100755 (executable)
--- a/gitweb.cgi
+++ b/gitweb.cgi
@@ -404,12 +404,13 @@ sub git_read_head {
        if (open my $fd, "-|", "$gitbin/git-rev-parse", "--verify", "HEAD") {
                my $head = <$fd>;
                close $fd;
-               chomp $head;
-               if ($head =~ m/^[0-9a-fA-F]{40}$/) {
-                       $retval = $head;
+               if (defined $head && $head =~ /^([0-9a-fA-F]{40})$/) {
+                       $retval = $1;
                }
        }
-       $ENV{'GIT_DIR'} = $oENV;
+       if (defined $oENV) {
+               $ENV{'GIT_DIR'} = $oENV;
+       }
        return $retval;
 }