Apply some v2.48 regression bugfixes (#5376)

Now that most of the Git contributors are back from the holidays, there
is an influx of bug fixes. This is precisely why I held off from rushing
Git for Windows v2.48.0 out the door.

These bug fixes are mostly taken from upstream's branches; In some
cases, though, I had to apply them directly from the Git mailing list
because they did not make it into git/git yet.

I deem those bug fixes necessary to get Git for Windows into a somewhat
healthy state again.

grep.c

@@ -1646,6 +1646,8 @@ static int grep_source_1(struct grep_opt *opt, struct grep_source *gs, int colle
 
 	bol = gs->buf;
 	left = gs->size;
+	if (left && gs->buf[left-1] == '\n')
+		left--;
 	while (left) {
 		const char *eol;
 		int hit;