Fix circle outline pattern not un-setting when removed
Description
Fixes issue where circle stroke pattern would not unset after being set.
Screenshots
Technical details
If strokePattern is null, default to the pattern [Dash(1)], which equals a full line.
There seems to be an issue in upstream where setting line pattern to null will not show the normal stroke again. I will report / fix this upstream as well, then we can remove the workaround here.