Change house GUI picker logic to be more like object GUI window.

Deselect house on object placement abort.
Set object placement on init or house selection.
Adjust display to still work even if no house selected,
by continuing to show the previous selection.

src/terraform_gui.cpp

@@ -614,7 +614,7 @@ struct ScenarioEditorLandscapeGenerationWindow : Window {
 				break;
 
 			case WID_ETT_PLACE_HOUSE: // Place house button
-				ShowBuildHousePicker(this);
+				ShowBuildHousePicker();
 				break;
 
 			case WID_ETT_INCREASE_SIZE:
@@ -682,10 +682,6 @@ struct ScenarioEditorLandscapeGenerationWindow : Window {
 				VpStartPlaceSizing(tile, VPM_X_AND_Y, DDSP_CREATE_DESERT);
 				break;
 
-			case WID_ETT_PLACE_HOUSE: // Place house button
-				PlaceProc_House(tile);
-				break;
-
 			default: NOT_REACHED();
 		}
 	}