[Maps] Border displayed when symbol size is set to 0

[nreese]

Steps to view issue:

1. create new map and add documents source from sample web logs
2. Set "Border width" to something like 6 so its easier to see the problem
3. Set "Symbol size" to zero. Notice how the borders are displayed even though there are no markers.

What should happen:
When symbol size is set to zero, borders should not be displayed

[elasticmachine]

Pinging @elastic/kibana-gis (Team:Geo)