Chart view preview mode is blank when full resolution is not available

@patchett2002 @utkarsh.ayachit @cory.quammen

Found on Linux with Python 3 ParaView binary.

Reproducible on MacOS 10.13.6 (2800x1800 display resolution) with python 2 binary from: https://www.paraview.org/paraview-downloads/download.php?submit=Download&version=v5.8&type=binary&os=macOS&downloadFile=ParaView-5.8.1-RC2-MPI-OSX10.12-Python2.7-64bit.dmg

For at least the line chart view, the preview mode is blank when the render window is not big enough to show the full resolution preview.

Steps to reproduce:

1. Close RenderView1 and open a line chart view
2. View -> Preview -> 1920x1080 (FHD) -> Ok
3. Resize the ParaView window until the 1920x1080 preview doesn't fit. The preview correctly shrinks to fit with the same aspect ratio, but the preview is now blank.