Handle errors more gracefully in get_display_refresh_rate

[alice-i-cecile]

There are a number of unwraps here:

bevy_framepace/src/lib.rs

Line 99 in fa6bb98

FramerateLimitParam::Auto => {

As far as I can tell, these could all just result in an early return instead, delaying the work if a monitor's frame rate could not be properly assessed.