Line.tagsBlocks would fail when text is blank and Line.process won't populate line.descent

[Akatmks]

Line.tagsBlocks would fail...

ILL-Aegisub-Scripts/modules/ILL/ILL/Ass/Line.moon

Lines 197 to 198 in 1e4fa86

	ascent = math.max ascent, line.height - line.descent
	descent = math.max descent, line.descent

Lua reported a runtime error:
    File "C:\fakepath\arch1t3cht Feature Release 12\automation\include\ILL\ILL\Ass\Line.moon", line 197
tagsBlocks
attempt to perform arithmetic on field 'descent' (a nil value)

...when text is blank and Line.process won't populate line.descent.

ILL-Aegisub-Scripts/modules/ILL/ILL/Ass/Line.moon

Lines 99 to 112 in 1e4fa86

	if textIsBlank
	textExtents = font\getTextExtents " "
	.width = 0
	.height = textExtents.height
	else
	textValue = .isShape and "" or .text_stripped
	textExtents = font\getTextExtents textValue
	textMetrics = font\getMetrics textValue
	.width = textExtents.width * video_x_correct_factor
	.height = textExtents.height
	.ascent = textMetrics.ascent
	.descent = textMetrics.descent
	.internal_leading = textMetrics.internal_leading
	.external_leading = textMetrics.external_leading