Fix for bug 1882282: Star glare clipping problem

Depth writes were left set to true after rendering comet tails, resulting in a star glare halos appearing to clip labels. Fixed by removing a glDepthMask(GL_TRUE) that shouldn't have been in the code at all.

src/celengine/render.cpp

@@ -6944,7 +6944,6 @@ void Renderer::renderCometTail(const Body& body,
     }
     glEnd();
 
-    glDepthMask(GL_TRUE);
     glEnable(GL_TEXTURE_2D);
     glEnable(GL_BLEND);