glslViewer - Blender add-on: do not re-calucalate frame buffer size. (MacBook M1)

[ssh4net]

Repro steps:

1. add a new object. For example Suzanna
2. enable IPR to render view to activate glslViewer rendering
3. drag to split the IPR viewport.

rendering will become distorted.

Possible issue: OpenGL does not recompute the changed framebuffer