Linux: Fix duplicate joystick objects

This fixes a regression introduced by
2c204ab52e.  This broke the check for
whether there is already a GLFW joystick object for a given input
device, making it always fail.

src/linux_joystick.c

@@ -128,7 +128,7 @@ static GLFWbool openJoystickDevice(const char* path)
 {
     for (int jid = 0;  jid <= GLFW_JOYSTICK_LAST;  jid++)
     {
-        if (_glfw.joysticks[jid].connected)
+        if (!_glfw.joysticks[jid].connected)
             continue;
         if (strcmp(_glfw.joysticks[jid].linjs.path, path) == 0)
             return GLFW_FALSE;