Do not start 2 new rasterizers on restart.

`restartService` kills the rasterizer and starts a new one, but the killed rasterizer also calls `startService` on its own `exit` event. As a result, every time `restartService` is called, 2 new rasterizers are spawned for the 1 killed.

Since the automatic `startService` on `exit` should remain intact, the `startService` within `restartService` should be removed.

This is probably related to what @lahdekorpi and @HaNdTriX report in #32.