Fix Dialog.bounds doesn't work as expected (fix aseprite#3898)

Prior to this fix, the 'Dialog:show()' function would override bounds
when they were defined before the 'show' command.
Also:
The Dialog.bounds getter now returns only the boundaries of
the current window.
The Dialog.bounds setter now does not allow empty bounds as input
argument.

src/app/script/dialog_class.cpp

@@ -340,6 +340,7 @@ int Dialog_show(lua_State* L)
       if (!rc.isEmpty()) {
         conn = dlg->window.Open.connect([dlg, rc]{
           dlg->setWindowBounds(rc);
+          dlg->window.setAutoRemap(false);
         });
       }
     }
@@ -1591,9 +1592,6 @@ int Dialog_set_data(lua_State* L)
 int Dialog_get_bounds(lua_State* L)
 {
   auto dlg = get_obj<Dialog>(L, 1);
-  if (!dlg->window.isVisible())
-    dlg->window.remapWindow();
-
   push_new<gfx::Rect>(L, dlg->getWindowBounds());
   return 1;
 }
@@ -1603,8 +1601,11 @@ int Dialog_set_bounds(lua_State* L)
   auto dlg = get_obj<Dialog>(L, 1);
   const auto rc = get_obj<gfx::Rect>(L, 2);
   if (rc) {
-    if (*rc != dlg->getWindowBounds())
+    // Empty rect isn't allowed.
+    if (*rc != dlg->getWindowBounds() && !rc->isEmpty()) {
       dlg->setWindowBounds(*rc);
+      dlg->window.setAutoRemap(false);
+    }
   }
   return 0;
 }

tests/scripts/dialogs.lua

@@ -0,0 +1,31 @@
+-- Copyright (C) 2023  Igara Studio S.A.
+--
+-- This file is released under the terms of the MIT license.
+-- Read LICENSE.txt for more information.
+
+if app.isUIAvailable then
+  dofile('./test_utils.lua')
+
+  -- Test dialog bounds
+  do
+    local dlg = Dialog("Bounds test")
+    local bounds = dlg.bounds
+    assert(bounds == Rectangle(0, 0, 0, 0))
+    dlg:show { wait=false }
+    local screenSize = Size(app.window.width, app.window.height)
+    bounds = dlg.bounds
+    assert(bounds.x == (screenSize.width - bounds.width) / 2)
+    assert(bounds.y == (screenSize.height - bounds.height) / 2)
+    dlg:close()
+  end
+
+  do
+    local rect = Rectangle(10, 20, 200, 50)
+    local dlg2 = Dialog("Bounds test 2")
+    dlg2.bounds = rect
+    assert(dlg2.bounds == rect)
+    dlg2:show { wait=false }
+    assert(dlg2.bounds == rect)
+    dlg2:close()
+  end
+end