Simplify handling of no-fill mode in man(7) by inspecting NODE_NOFILL

Simplify handling of no-fill mode in man(7) by inspecting NODE_NOFILL
at the beginning of the node handler, in the same way as it is done
in the mdoc(7) node handler.

As a side effect, this also fixes a bug: if an input line contained
nothing but an escape sequence producing no output whatsoever (for
example, \fR), the old code incorrectly emitted a blank line anyway,
whereas the new code only emits such a blank link if the input line
actually produces output (even invisible zero-width output). To make
the distinction, the ASCII_NBRZW -> lastcol -> term_newln() mechanism
established in term.c rev. 1.149 is used.