Fix NullReferenceException in HamburgerMenu when space/enter key is hold (#1154)
Fix NullReferenceException in HamburgerMenu when space/enter key is hold (#1154)

* Fix NavCommand.Execute is invoked on HamburgerButton when Space key is hold

* Fix spacing

callummoffat/Template10,liptonbeer/Template10,devinfluencer/Template10,teamneusta/Template10,dkackman/Template10,liptonbeer/Template10,teamneusta/Template10,SimoneBWS/Template10,GFlisch/Template10,GFlisch/Template10,SimoneBWS/Template10,Viachaslau-Zinkevich/Template10,callummoffat/Template10,Windows-XAML/Template10,dkackman/Template10,devinfluencer/Template10,mvermef/Template10,MichaelPetrinolis/Template10,dg2k/Template10,Viachaslau-Zinkevich/Template10,MichaelPetrinolis/Template10