Be careful before using buffer parameters in colAlign

Be careful before using buffer parameters in colAlign

Make InsetGrid::colAlign a normal method and make it check whether
buffer is valid before using it. This avoids crashes as we have seen
in 2.3.3 (see e.g. #11686).

There is still an assertion so that failure is noticeable before release.

(cherry picked from commit 44816adce634c8a06c1ff0591adbcf042ec4c072)