Ensure duplicated file pointer is closed

[radarhere]

Resolves #5936. Ensures that the file pointer duplicated in TiffImagePlugin is closed, rather than counting on libtiff to do it.

Pillow/src/PIL/TiffImagePlugin.py

Lines 1186 to 1188 in eff6c34

	# libtiff closes the file descriptor, so pass in a dup.
	try:
	fp = hasattr(self.fp, "fileno") and os.dup(self.fp.fileno())

I haven't added a test for this, since the issue involves hitting the limit on the number of open files.