fix font file name contains space

[Pagliacii]

resolve #273

[jlu5]

(Strangely enough, in my testing I'm having issues with loading custom fonts both with and without this patch. Will need to verify this further)

[dnk]

it is need to apply the same change to https://github.com/varietywalls/variety/blob/master/variety/Options.py#L682

grep FONT_NAME . -RI
./variety/VarietyWindow.py: clock_filter = clock_filter.replace("%CLOCK_FONT_NAME", clock_font_name)
./variety/VarietyWindow.py: clock_filter = clock_filter.replace("%DATE_FONT_NAME", date_font_name)
./variety/Options.py: self.clock_filter = "-density 100 -font fc-match -f '%{file[0]}' '%CLOCK_FONT_NAME' -pointsize %CLOCK_FONT_SIZE -gravity SouthEast -fill '#44' -annotate 0x0+[%HOFFSET+58]+[%VOFFSET+108] '%H:%M' -fill white -annotate 0x0+[%HOFFSET+60]+[%VOFFSET+110] '%H:%M' -font fc-match -f '%{file[0]}' '%DATE_FONT_NAME' -pointsize %DATE_FONT_SIZE -fill '#44' -annotate 0x0+[%HOFFSET+58]+[%VOFFSET+58] '%A, %B %d' -fill white -annotate 0x0+[%HOFFSET+60]+[%VOFFSET+60] '%A, %B %d'"
./data/config/variety.conf:clock_filter = "-density 100 -font fc-match -f '%{file[0]}' '%CLOCK_FONT_NAME' -pointsize %CLOCK_FONT_SIZE -gravity SouthEast -fill '#44' -annotate 0x0+[%HOFFSET+58]+[%VOFFSET+108] '%H:%M' -fill white -annotate 0x0+[%HOFFSET+60]+[%VOFFSET+110] '%H:%M' -font fc-match -f '%{file[0]}' '%DATE_FONT_NAME' -pointsize %DATE_FONT_SIZE -fill '#44' -annotate 0x0+[%HOFFSET+58]+[%VOFFSET+58] '%A, %B %d' -fill white -annotate 0x0+[%HOFFSET+60]+[%VOFFSET+60] '%A, %B %d'"