Bug in gitk search box

To reproduce:

* Open gitk in any repository, the Git one seems to work fine.
* Type a string that it won't find into the search box, like 'asdfasdf'.
* Click find.

You'll get:

can't read "commitdata(e83c5163316f89bfbde7d9ab23ca2e25604af290)": no such element in array
can't read "commitdata(e83c5163316f89bfbde7d9ab23ca2e25604af290)": no such element in array
    while executing
"doesmatch $commitdata($id)"
    (procedure "findmore" line 21)
    invoked from within
"findmore"
    ("eval" body line 1)
    invoked from within
"eval $script"
    (procedure "dorunq" line 9)
    invoked from within
"dorunq"
    ("after" script)

Where the SHA1 is always the earliest SHA1 in the rev-list gitk is examining.

After this happens you get a "busy cursor" when hovering over most of gitk, and you can't search again until gitk is restarted.

-bcd