Subject: bug#28527: unexpected behaviour of char-after if argument is marker that don't point to the current buffer

From: Fritz Stelzer <[email-masked]>
Date: Wed, 20 Sep 2017 15:29:07 +0200

When the argument for char-after is a marker, the function gets bytepos
from the buffer the marker is pointing to by calling marker_byte_position.
But then pos_byte is compared to BEGV_BYTE and ZV_BYTE that use the current
buffer. At the end of the function, pos_byte is passed to FETCH_CHAR, which
also operates on the current buffer.