cherry-pick: Only fetch if remote branch doesn't exist

[jerry-skydio]

Cherry-pick was updated to fetch if the branch doesn't exist, but this could fetch unnecessarily if the remote branch exists locally but namespaced in the remote.

Make this more clear with 3 paths:

• branch exists locally
• branch doesn't exist but remote version of it does (no fetch needed)
• neither of the above exists, will attempt to fetch

[jerry-skydio]

Reviews in this chain: └https://github.com/Skydio/revup/pull/169 cherry-pick: Only fetch if remote branch doesn't exist

[jerry-skydio]

#	head	base	diff	date	summary
0	2262b049	c4ace457	diff	Mar 13 14:51 PM	1 file changed, 15 insertions(+), 9 deletions(-)
1	5547b895	c4ace457	diff	Mar 13 14:52 PM	1 file changed, 1 insertion(+), 1 deletion(-)

[jerry-skydio]

no :disappointed: i'll think about this some more since I agree its objectively more important to be able to pick up changes vs saving ~.5s