GdkWaylandWindow: window_update_scale: Don't reset scale to 1 with no outputs

When there is on_monitors_changed called on GdkWindow which doesn't have
any outputs on its impl->display_server.outputs list, the scale was being
reset to 1, causing GtkPopovers to set their scale to 1 and having blurry
appearance on hidpi screens.
2 jobs for hidpi-popovers in 6 seconds (queued for 16 seconds)
latest
Status Job ID Name Coverage
  Build
failed #276533
build

00:00:06

manual #276534
win32 allowed to fail manual
msys2-mingw32
 
Name Stage Failure
failed
build Build
Running with gitlab-runner 12.10.2 (c5874a4b)
on Skylake 8 Core AMD64 YEzXj2xz
Preparing the "docker" executor
Using Docker executor with image registry.gitlab.gnome.org/gnome/gtk/gtk-3-24:v1 ...
Pulling docker image registry.gitlab.gnome.org/gnome/gtk/gtk-3-24:v1 ...
ERROR: Job failed: Error response from daemon: manifest for registry.gitlab.gnome.org/gnome/gtk/gtk-3-24:v1 not found: manifest unknown: manifest unknown (docker.go:198:1s)