Fix unpressable buttons

doc/classes/BaseButton.xml

@@ -50,7 +50,7 @@
 		<member name="button_group" type="ButtonGroup" setter="set_button_group" getter="get_button_group">
 			The [ButtonGroup] associated with the button. Not to be confused with node groups.
 		</member>
-		<member name="button_mask" type="int" setter="set_button_mask" getter="get_button_mask" enum="MouseButtonMask" default="0">
+		<member name="button_mask" type="int" setter="set_button_mask" getter="get_button_mask" enum="MouseButtonMask" default="1">
 			Binary mask to choose which mouse buttons this button will respond to.
 			To allow both left-click and right-click, use [code]MOUSE_BUTTON_MASK_LEFT | MOUSE_BUTTON_MASK_RIGHT[/code].
 		</member>

scene/gui/base_button.h

@@ -46,7 +46,7 @@ public:
 	};
 
 private:
-	BitField<MouseButtonMask> button_mask;
+	BitField<MouseButtonMask> button_mask = MouseButtonMask::LEFT;
 	bool toggle_mode = false;
 	bool shortcut_in_tooltip = true;
 	bool was_mouse_pressed = false;