plugins/zoom: Simplify initial zoom initialization
The initial zoom level can be read in the constructor instead of initializing m_sourceZoom to -1.
Also, setTargetZoom() is not necessary because zoomTo() is going to call it too.
The initial zoom level can be read in the constructor instead of initializing m_sourceZoom to -1.
Also, setTargetZoom() is not necessary because zoomTo() is going to call it too.