preprocessor: Fix column adjustment [PR 99446]

This ICE was because when adjusting a column offset we could advance
into a linemap for a different file.  We only checked the next line
map was not for a line further advanced in any file, forgetting that
it could be for an earlier line in a different file.  The testcase
needed adjusting as column 512 was unrepresentable, once that was
taken into consideration.

	PR preprocessor/99446
	libcpp/
	* line-map.c (line-map.c): Do not advance to linemaps for
	different files.
	gcc/testsuite/
	* g++.dg/diagnostic/pr72803.C: Adjust expected column.