Static image marker fixes

[freszu]

New version of Mapbox static map utils 3.x caused a few issues for us that should solve it.
Old working link from 2.x:

https://api.mapbox.com/styles/v1/username/styleId/static/pin-l+ff0000(-115.255990,36.263328),pin-l+ff0000(-115.255990,36.263328)/auto/800x300?access_token=token&logo=false

New failing link from 3.x:

https://api.mapbox.com/styles/v1/username/styleId/static/pin-l-ff0000(-115.255990,36.263328),null/auto/800x300?access_token=token&logo=false

PR contains:

• Fix string format for color
• remove useless null check - TextUtils already does that
• Fix wrong link generated when 2 pins are in the same location have same size and color - old behaviour was creating proper link, new one fails silently generating illegal url by placing null as second pin. This was the result of indexOf call which was also removed because its a waste of cpu cycles.

[osana]

Thank you for your contribution. I will port your PR to be merged

[osana]

merged by #839