Fix C++ exception error in Significance 'make style from act. line' stuff function.

[moex3]

Aegisub version: Aegisub 9676-migration02-168b6f679

Example line:
Dialogue: 0,0:02:00.60,0:02:00.64,Default,,0,0,0,,{\b1}test

When trying to make a new style from this line using Significance, it fails with:
Lua reported a runtime error: C++ exception

Changing the line insertion code to subs[-i] = sr in line 816, reveals another error message:
Invalid or missing field 'bold' in 'style' class subtitle line (expected boolean)

Something must have changed, and now Aegisub expects those boolean fields to actually be boolean type. I fixed it by converting those 4 boolean types to an actual boolean typed value.
I also fixed the margins, because it never used the margins from the style even if the margins on the lines were left 0.