libext2fs: fix data read corruption in ext2fs_file_read_inline_data

libext2fs: fix data read corruption in ext2fs_file_read_inline_data

Fix numerous problems in the function that reads data from an inlinedata
file:

 - Reads starting after isize should be returned as short reads.
 - Reads past the end of the inline data should return zeroes.
 - Reads from the inline data buffer must not exceed isize.

Cc: linux-ext4@vger.kernel.org # v1.43
Fixes: 54e880b870f7fe ("libext2fs: handle inline data in read/write function")
Signed-off-by: Darrick J. Wong <djwong@kernel.org>
Link: https://lore.kernel.org/r/20250717145933.GI2672022@frogsfrogsfrogs
Signed-off-by: Theodore Ts'o <tytso@mit.edu>