Fix zero relative motion event when clicking in MOUSE_MODE_CAPTURED

platform/windows/os_windows.cpp

@@ -458,7 +458,7 @@ LRESULT OS_Windows::WndProc(HWND hWnd, UINT uMsg, WPARAM wParam, LPARAM lParam)
 					*/
 				}
 
-				if (window_has_focus && main_loop)
+				if (window_has_focus && main_loop && mm->get_relative() != Vector2())
 					input->parse_input_event(mm);
 			}
 			delete[] lpb;