[multi-monitor] On NVidia, launcher best placed on left-most monitor (not primary)

[Gerry Boland]

On a Multi-monitor setup, using NVidia graphics & closed-driver.

It is possible to have no primary monitor set

One can set up two screens as follows:
- on the right, a laptop screen (most likely seen as first by the driver)
- on the left, an external monitor
Currently Unity2D will place launcher on left of the 'first' monitor.

In this case, it makes best sense to have launcher placed on the left-most screen. (Unity does this)

If you set the primary monitor in nvidia-settings, then all works ok.