More accurate logic for node's remove view method

Provide an fix like:

https://github.com/lite-xl/lite-xl/pull/526

but use instead the is_primary_node property and the context
property.

We align the logic to the one used in the close_all_views method.

The approach using get_locked_size was the old approach using by
rxi's lite but it should no longer be used to determine if a node
if part of the application UI or part of the document's view.

data/core/rootview.lua

@@ -128,6 +128,18 @@ function Node:split(dir, view, locked, resizable)
   return self.b
 end
 
+
+function Node:is_application()
+  if self.type == "leaf" then
+    for i = 1, #self.views do
+      if self.views[i].context == "application" then return true end
+    end
+  else
+    return self.a:is_application() or self.b:is_application()
+  end
+end
+
+
 function Node:remove_view(root, view)
   if #self.views > 1 then
     local idx = self:get_view_idx(view)
@@ -142,7 +154,7 @@ function Node:remove_view(root, view)
     local parent = self:get_parent_node(root)
     local is_a = (parent.a == self)
     local other = parent[is_a and "b" or "a"]
-    if other:get_locked_size() then
+    if self.is_primary_node and other:is_application() then
       self.views = {}
       self:add_view(EmptyView())
     else