Removed unused rename icon
Avoid hang on Mac OS X when drawing certain ellipse objects

Trying to draw an ellipse with 0-width is causing a hang in
CoreGraphics when drawing the path requested by the
QCoreGraphicsPaintEngine. Draw them as rectangle instead.

In the isometric renderer, a rectangle is drawn as well anyway,
so the drawing of a 0-width ellipse is simply avoided.

Fixes #613