Also needs to be fixed in 9.x.x/Release.

Repro steps:
1. Open Shadergraph
2. Click drag lower right corner of the Master Preview to the upper left
Expected result: the master preview stops before it gets too small
Actual result: the master preview can be shrunk down to a single pixel and can not be expanded again

Note: this problem will be exacerbated when the bug where window sizes aren't saved to user preferences is fixed, which will result in a master preview that can be made unusable until the user preferences folder is deleted.