Fix indentation of paragraphs after an environment.

Fix indentation of paragraphs after an environment.

When deciding whether a paragraph should be indented or not, LyX
only takes into account default layouts. This is wrong, because
an environment could be nested into another one and thus a following
paragraph would not be "default". With this patch all paragraphs
after an environment are correctly indented, independently of
whether their layouts are "default" or not.
The latex output (which was modeled following the previous wrong
assumption) is also correspondingly adapted.