Fix unintended SpinBox mouse capture

(cherry picked from commit ae2cf8eb382db2b6c8d597f0015db976eb433500)

scene/gui/spin_box.cpp

@@ -300,7 +300,6 @@ SpinBox::SpinBox() {
 	line_edit->connect("text_entered", this, "_text_entered", Vector<Variant>(), CONNECT_DEFERRED);
 	line_edit->connect("focus_exited", this, "_line_edit_focus_exit", Vector<Variant>(), CONNECT_DEFERRED);
 	line_edit->connect("gui_input", this, "_line_edit_input");
-	drag.enabled = false;
 
 	range_click_timer = memnew(Timer);
 	range_click_timer->connect("timeout", this, "_range_click_timeout");

scene/gui/spin_box.h

@@ -53,11 +53,11 @@ class SpinBox : public Range {
 	void _line_edit_input(const Ref<InputEvent> &p_event);
 
 	struct Drag {
-		float base_val;
-		bool allowed;
-		bool enabled;
+		float base_val = 0;
+		bool allowed = false;
+		bool enabled = false;
 		Vector2 capture_pos;
-		float diff_y;
+		float diff_y = 0;
 	} drag;
 
 	void _line_edit_focus_exit();