Fixed regression introduced by a6fa3e37.
a6fa3e37 changed the logic in vtkWin32OpenGLRenderWindow::CleanUpRenderers(). That method was used when swithcing from offscreen to onscreen. That resulted in the renderers not having correct references to render window after switching from offscreen to onscreen context causing dashboard failures on ParaView dashboards. This fixes that issue. Since the a6fa3e37 changed the logic in CreateOffScreenDC() by not using CleanUpRenderers() to reset renderers, it makes sence to change the logic in ResumeScreenRendering() to not use CleanUpRenderers() for resetting renderers as well. Change-Id: I32e58854fa8720c99212cee5d7a2652f11dc9b21