screen-cast: Fix window recording on HiDPI
Using the same scale for the window as the logical monitor only works correctly when having the experimental 'scale-monitor-framebuffer' feature enabled. Without this experimental feature, the stream will contain a black screen, where the actual window only takes a small part of it.
Therefore, use a scale of 1 for the non- experimental case.
Patch is based on commit 3fa6a92c.