Raise FileNotFoundError when opening an empty path

[radarhere]

Resolves #9047

The following code didn't consider the possibility of an empty filename being passed in by the user, and tries to treat it as a file handle instead.

Pillow/src/PIL/Image.py

Lines 3510 to 3518 in 2b39f75

	filename: str | bytes = ""
	if is_path(fp):
	filename = os.fspath(fp)
	if filename:
	fp = builtins.open(filename, "rb")
	exclusive_fp = True
	else:
	fp = cast(IO[bytes], fp)

This fixes that.