Fix bug #7050: Assert when using DecimalAlignment in tables.

Fix bug #7050: Assert when using DecimalAlignment in tables.

The problem is/was that when copying an InsetTableCell?, the macrocontext_position_ and the buffer_ were not copied. That's why in InsetTabular?@splitCell@521 and in InsetTabular::TeXRow() and in InsetTabular::metrics we manually copy this into the new object.

However, splitCell() returns the object by-value. So, when we call

InsetTableCell tail = splitCell(head, column_info[c].decimal_point, hassep);

the new object is copied into tail and we lose the buffer_ and macro_contextposition. Later we will crash.

What does *nix in this case ? Apparently they don't make buffer and/or macro_contextposition 0.

git-svn-id: svn://svn.lyx.org/lyx/lyx-devel/trunk@37072 a592a061-630c-0410-9148-cb99ea01b6c8