SVG font input empty chars not output to SFD or fonts

Magic flag widthset was not being set for input glyphs upon parsing
from SVG font files.  This flag is used by sfd.c routine SFDOmit()
to judge whether a character was significant enough to be output.

Upon first input from SVG font file, empty glyphs (not containing any
drawing instructions / spline info) would appear in character view
(as X'd boxes).  But these would not be output to a new SFD file or
any generated fonts.  Restarting FF using the previous SFD file as
input would find none of the empty characters - they'd disappeared.

This would affect such glyphs as '.null', 'space', and maybe
'nomarkingreturn'.

Fix adds one line to set flag into svg.c routine SVGParseGlyphArgs().
Merge pull request #1480 from tshinnic/sfd_empty_char

SVG font input empty chars not output to SFD or fonts