Don't pane focus when pane model is destroyed
Don't pane focus when pane model is destroyed

This avoids a non-failure error message when resetting the environment
in some specs.

kevinrenaers/atom,decaffeinate-examples/atom,brettle/atom,stinsonga/atom,sotayamashita/atom,AlexxNica/atom,FIT-CSE2410-A-Bombs/atom,liuderchi/atom,CraZySacX/atom,t9md/atom,atom/atom,decaffeinate-examples/atom,andrewleverette/atom,liuderchi/atom,Arcanemagus/atom,t9md/atom,FIT-CSE2410-A-Bombs/atom,CraZySacX/atom,liuderchi/atom,PKRoma/atom,AlexxNica/atom,ardeshirj/atom,decaffeinate-examples/atom,Mokolea/atom,brettle/atom,stinsonga/atom,AlexxNica/atom,brettle/atom,stinsonga/atom,sotayamashita/atom,Arcanemagus/atom,Mokolea/atom,ardeshirj/atom,kevinrenaers/atom,PKRoma/atom,kevinrenaers/atom,atom/atom,ardeshirj/atom,Mokolea/atom,Arcanemagus/atom,andrewleverette/atom,CraZySacX/atom,FIT-CSE2410-A-Bombs/atom,decaffeinate-examples/atom,atom/atom,andrewleverette/atom,PKRoma/atom,liuderchi/atom,t9md/atom,sotayamashita/atom,stinsonga/atom