Git error: previous rebase directory .git/rebase-apply still exists but mbox given

git am --abort

worked for me, but git rebase --abort did not.

What happened: I tried to apply a patch but it had been corrupted (likely by Gmail copy pasting in body):

git am bad.patch

And Git said:

Applying: python: fix Linetable case to LineTable in docstrings and comments
fatal: corrupt patch at line 56
Patch failed at 0001 python: fix Linetable case to LineTable in docstrings and comments
The copy of the patch that failed is found in:
   /home/ciro/git/binutils-gdb/src/.git/rebase-apply/patch
When you have resolved this problem, run "git am --continue".
If you prefer to skip this patch, run "git am --skip" instead.
To restore the original branch and stop patching, run "git am --abort".

Note how git gives out the solution: To restore the original branch and stop patching, run "git am --abort".

Then I obviously ignored the message, and tried a fixed version immediately:

git am good.patch

and got the error.

Ok, it turned out I needed to delete the directory .git/rebase-apply. It works after that (or at least gives me different errors, saying the email is wrong again). I still have no idea what the error actually means or why there was an error.

Edit: As the comments below suggest, git am --abort or git rebase --abort might be a better way to fix the problem, but I have not tested it.