Three t4150 tests does not work as expected

Hi,

I noticed that the following three t4150 tests probably does not work as expected:

- record as an empty commit when meeting e-mail message that lacks a patch
- record an empty patch as an empty commit in the middle of an am session
- create an non-empty commit when the index IS changed though "--allow-empty" is given

All of them does something like:

	git show HEAD --format="%B" >actual
	grep -f actual expected

While the 'actual' file usually contains something like (four lines between the 'cut' markers):

-------------------------- cut -------------------------- empty commit

-- 2.45.1

-------------------------- cut --------------------------

IOW, there are two empty lines there. Because of that the grep gets an empty RE from the 'actual' file and so it matches everything that comes in the 'expected' file.

Is this the expected behavior?

Thank you.