git wrapper: Make while loop more reader-friendly

git wrapper: Make while loop more reader-friendly

It is not a good practice to prefer performance over readability in
something as performance uncritical as finding the trailing slash
of argv[0].

So avoid head-scratching by making the loop user-readable, and not
hyper-performance-optimized.

Signed-off-by: Johannes Schindelin <johannes.schindelin@gmx.de>
Signed-off-by: Junio C Hamano <gitster@pobox.com>