Focus root view if previously focused element is no longer attached

This can be the case when a select list is triggered while a different
select list is already open and so the second list to open has no
element to restore focus to when it closes.

src/app/select-list.coffee

@@ -151,7 +151,10 @@ class SelectList extends View
     @previouslyFocusedElement = $(':focus')
 
   restoreFocus: ->
-    @previouslyFocusedElement?.focus()
+    if @previouslyFocusedElement?.isOnDom()
+      @previouslyFocusedElement.focus()
+    else
+      rootView.focus()
 
   cancelled: ->
     @miniEditor.setText('')

src/packages/go-to-line/lib/go-to-line-view.coffee

@@ -36,6 +36,11 @@ class GoToLineView extends View
     @detaching = true
     @miniEditor.setText('')
 
+    if @previouslyFocusedElement?.isOnDom()
+      @previouslyFocusedElement.focus()
+    else
+      rootView.focus()
+
     super
 
     @detaching = false