Fix editor background jump (#2182)

Author: mrkubax10

src/editor/editor.cpp

@@ -80,7 +80,7 @@ Editor::is_active()
     return true;
   } else {
     auto* self = Editor::current();
-    return self && !self->m_leveltested;
+    return self && !self->m_leveltested && self->m_after_setup;
   }
 }
 
@@ -105,6 +105,7 @@ Editor::Editor() :
   m_sector(),
   m_levelloaded(false),
   m_leveltested(false),
+  m_after_setup(false),
   m_tileset(nullptr),
   m_widgets(),
   m_overlay_widget(),
@@ -615,13 +616,15 @@ Editor::leave()
 {
   MouseCursor::current()->set_icon(nullptr);
   Compositor::s_render_lighting = true;
+  m_after_setup = false;
 }
 
 void
 Editor::setup()
 {
   Tile::draw_editor_images = true;
   Sector::s_draw_solids_only = false;
+  m_after_setup = true;
   if (!m_levelloaded) {
 
 #if 0

src/editor/editor.hpp

@@ -198,6 +198,7 @@ class Editor final : public Screen,
 
   bool m_levelloaded;
   bool m_leveltested;
+  bool m_after_setup; // Set to true after setup function finishes and to false after leave function finishes
 
   TileSet* m_tileset;