Fix inverted relative mouse motion in HTML5 export

(cherry picked from commit 640d8cc5d2749bbe29a6a85d076a7bdf264d146b)

platform/javascript/os_javascript.cpp

@@ -189,8 +189,8 @@ static EM_BOOL _mousemove_callback(int event_type, const EmscriptenMouseEvent *m
 	ev.mouse_motion.global_x = ev.mouse_motion.x = mouse_event->canvasX;
 	ev.mouse_motion.global_y = ev.mouse_motion.y = mouse_event->canvasY;
 
-	ev.mouse_motion.relative_x = _input->get_mouse_pos().x - ev.mouse_motion.x;
-	ev.mouse_motion.relative_y = _input->get_mouse_pos().y - ev.mouse_motion.y;
+	ev.mouse_motion.relative_x = ev.mouse_motion.x - _input->get_mouse_pos().x;
+	ev.mouse_motion.relative_y = ev.mouse_motion.y - _input->get_mouse_pos().y;
 
 	_input->set_mouse_pos(Point2(ev.mouse_motion.x, ev.mouse_motion.y));
 	ev.mouse_motion.speed_x = _input->get_mouse_speed().x;
@@ -310,8 +310,8 @@ static EM_BOOL _touchmove_callback(int event_type, const EmscriptenTouchEvent *t
 		ev.mouse_motion.button_mask = _input->get_mouse_button_mask() >> 1;
 		ev.mouse_motion.global_x = ev.mouse_motion.x = touch_event->touches[lowest_id_index].canvasX;
 		ev.mouse_motion.global_y = ev.mouse_motion.y = touch_event->touches[lowest_id_index].canvasY;
-		ev.mouse_motion.relative_x = _input->get_mouse_pos().x - ev.mouse_motion.x;
-		ev.mouse_motion.relative_y = _input->get_mouse_pos().y - ev.mouse_motion.y;
+		ev.mouse_motion.relative_x = ev.mouse_motion.x - _input->get_mouse_pos().x;
+		ev.mouse_motion.relative_y = ev.mouse_motion.y - _input->get_mouse_pos().y;
 
 		_input->set_mouse_pos(Point2(ev.mouse_motion.x, ev.mouse_motion.y));
 		ev.mouse_motion.speed_x = _input->get_mouse_speed().x;