[bot_update] Resolve revision only if patching
[bot_update] Resolve revision only if patching

If bot_update is not patching, it shouldn't look into gitiles patch
information.

R=ehmaldonado@google.com

Bug: 1147625
Recipe-Nontrivial-Roll: build
Change-Id: I111f0dc1c36d588341c02930bf1cda1f5b8cc2e7
Reviewed-on: https://chromium-review.googlesource.com/c/chromium/tools/depot_tools/+/2644199
Reviewed-by: Edward Lesmes <d05609f027dc667cc37492b1dc1bdea5d60fa82a@chromium.org>
Commit-Queue: Josip Sokcevic <4606aec58cba917397ff2e4738f995e4758694f8@google.com>

CoherentLabs/depot_tools,CoherentLabs/depot_tools