Rewording a commit at the beginning of a long branch can take very long;
without this change, the commit message panel would stay visible with a blinking
cursor during that time, which is very confusing.
This has the slight downside that it will say "Rebasing" in the lower right
corner until the operation is done; but we already have this problem when doing
custom patch operations, or dropping changes from a commit, so it's not new, and
we can think about how to fix all these another time.
c18d8af9f4