fix: SG-42902: Fix seg fault on Linux when displays are stacked in the system settings

[eloisebrosseau]

SG-42902: Fix seg fault on Linux when displays are stacked in the system settings

Summarize your change.

Prevent accessing the screen index of a secondary monitor if it invalid (i.e. -1).

Describe the reason for the change.

Open RV would crash when trying to launch on Linux if a secondary monitor was stacked under the primary monitor in the system settings on Linux. The issue was introduced by the upgrade to Qt6 where screenNumber() and screenGeometry() were now deprecated and respectively replaced with the lambda function getScreenFromPoint() and the Qt function geometry(). With the previous implementation, Qt was falling back to using index 0 (i.e. the primary screen) if the index of the screen was invalid. However, I believe we are better by simply not computing any calculation if the screen index is -1 as comparing the values between the same screen wouldn't do anything.

Note that I also moved getScreenFromPoint() closer to where it was actually used to make the code a little bit more readable.

Describe what you have tested and on which operating system.

Tested different configuration of arranging displays in the System Settings was tested on Linux, macOS and Windows.

[bernie-laberge]

LGTM and pretty safe
I would merge it without view testing once code reviewed.