Fix potential crash when using DesignableGradient
Fix potential crash when using DesignableGradient

seanwoodward/IBAnimatable,IBAnimatable/IBAnimatable,IBAnimatable/IBAnimatable,JakeLin/IBAnimatable,JakeLin/IBAnimatable,seanwoodward/IBAnimatable,alexiosdev/IBAnimatable,alexiosdev/IBAnimatable,IBAnimatable/IBAnimatable