Fix bezier_render_(fill|stroke)

The previous version did not correctly draw the remaining parts
after the main loop. The bug stayed unnoticed with the complex
curves for "Standard - Outline", but became very visible with
the path-variations.svg with it simple holes being blanked.
svg: more path-variations including CSS

also some more comments
Fix build w/o ENABLE_NLS

recent use of NC_ was not covered by Dia's own intl.h
Increased robustness for create_standard_path_from_object()

Don't try to create empty path also some comment about
potential future development.
Fix compilation warning

Signed-off-by: Hans Breuer <hans@breuer.org>