[UI bug] When "[Events] -> Margin < 0", Margin will be not displayed in UI

[op200]

e.g.

[Events]
Format: Layer, Start, End, Style, Name, MarginL, MarginR, MarginV, Effect, Text
Dialogue: 0,0:00:02.96,0:00:06.52,abc,,0,0,-1,,123456

(The MarginV == -1)