[sailfish-browser] Reset MozWindow upon close event if all tabs have been closed. Fixes JB#33457
[sailfish-browser] Reset MozWindow upon close event if all tabs have been closed. Fixes JB#33457

Exit was not correctly handle on Gecko 38 if all tabs were closed (last view)
before closing the browser from the switcher.

sailfishos/sailfish-browser,sailfishos/sailfish-browser,sailfishos/sailfish-browser,sailfishos/sailfish-browser,sailfishos/sailfish-browser