Toggle control_name in <floater/>'s like booleans for visibility, if they exist.

Look out for this in the UI Overhaul merge, this is gonna clash big time.

indra/llui/llfloater.cpp

@@ -571,6 +571,9 @@ void LLFloater::open()	/* Flawfinder: ignore */
 		setVisibleAndFrontmost(mAutoFocus);
 	}
 
+	if (!getControlName().empty())
+		setControlValue(true);
+
 	onOpen();
 }
 
@@ -633,6 +636,9 @@ void LLFloater::close(bool app_quitting)
 			}
 		}
 
+		if (!app_quitting && !getControlName().empty())
+			setControlValue(false);
+
 		// Let floater do cleanup.
 		onClose(app_quitting);
 	}