Added check for editor state during Edit menu display (ref #70).

This avoids a strange run-time error on Linux that appears to be caused
by UpdateUI checks in Edit menu for editor object that is out of use.

src/editor/editor.lua

@@ -458,7 +458,7 @@ function IndicateAll(editor, lines, linee)
 
   -- this function can be called for an editor tab that is already closed
   -- when there are still some pending events for it, so handle it.
-  if not pcall(function() return editor:GetId() end) then return end
+  if not pcall(function() editor:GetId() end) then return end
 
   -- if markvars is not set in the spec, check for functions-only indicators
   if not (editor.spec and editor.spec.markvars) then

src/editor/menu_edit.lua

@@ -47,7 +47,7 @@ local function getControlWithFocus()
        or ide.osname == 'Macintosh' and
          ctrl:GetParent():GetId() == e:GetId()) then editor = e end
   end
-  return editor
+  return pcall(function() editor:GetId() end) and editor or nil
 end
 
 local function onUpdateUIEditMenu(event)