Sketch: Opacity and fill percentage differ

[WCarlsson]

Describe the bug
When using the sketch plugin and changing opacity to 0% the fill percentage, which normally follow the opacity percantage, change to 100%. If the fill options is minimized it shows only 100% leading to possible confusion for users
If you draw a polygon it is fully transparent as expected so it is only the fill percentage that is misleading.

To Reproduce
Steps to reproduce the behavior:

1. Go to a current version of Hajk (tested on 3.10 and develop)
2. Start the sketch plugin
3. Draw a object where you can set opacity and set it to 0%
4. See fill percentage mimic opacity percentage until 0% when it jumps to 100%

Expected behavior
Percentage of Fill should follow opacity

Screenshots