gitweb:fix tests on uninitialized hash indexes to avoid uninitialized value warnings in server log

Hi,

It's happened that I tried to solve lots of meaningless warnings
in web server error log.

I think it makes no sense to spam error log with warnings about
uninitialized value when trying to run careless tests on undefined
hash indexes.

This is a simple fix that I did long ago that check carefully the
index before running tests on it.

I added myself as warning fix author as well.

My goal is to avoid re-applying the patch on each distribution update.

The warning message fixed in web server error log :
Use of uninitialized value $params{"action"} in string eq at gitweb.cgi
line 1377

Pull request was done here against "maint" branch :
https://github.com/gitgitgadget/git/pull/617

Pull request was done here against "master" branch if required :
https://github.com/git/git/pull/767

The change patch is attached if required.

May you plz merge my change ?

Best regards

Raphaël Gertz [off-list ref]:
 gitweb/README: add myself as warning fix author
 gitweb/gitweb.perl: fix careless test on undefined hash indexes

 gitweb/README      | 3 +++
 gitweb/gitweb.perl | 4 ++--
 2 files changed, 5 insertions(+), 2 deletions(-)

Signed-off-by: Raphaël Gertz <redacted>