Bug 1774201 - Stop skipping ReinitRendering if previous attempt failed....

Bug 1774201 - Stop skipping ReinitRendering if previous attempt failed. r=gfx-reviewers,aosmond a=pascalc

In bug 1728062 we made it so that we that we skip
BrowserChild::ReinitRendering if the BrowserChild is not connected to
a compositor. This was in order to avoid initializing the compositor
for windowless browsers.

However, in cases where the GPU process dies before an initial
InitRendering has completed, then the BrowserChild will also be left
not connected to a compositor, with mLayersConnected == Some(false).
ReinitRendering will be called once the new GPU process has been
launched, but due to this condition we will exit early, and the tab
will be left in an unusable state.

To fix this, this patch changes the early return condition to only
check for mLayersConnected.isNothing(), ie we never even attempted to
initialize rendering. When it is Some(false), ie we attempted and
failed, then ReinitializeRendering is still executed.

Differential Revision: https://phabricator.services.mozilla.com/D149619