Don't use the Unloaded event to dispose the stream

[x000000]

When we use a gif inside of TabControl it dispose stream upon tab change and when we switch tab back it won't load an animation.

[thomaslevesque]

Hi, thanks for the bug report. I'll look into it when I can, but I'm quite busy with other things, so I can't promise a quick fix.

[will-scc]

I think I've stumbled across this issue, or a very similar one, after setting CacheFramesInMemory and having the image visibility set to Hidden. It throws 4 System.ObjectDisposedException exceptions.

If I get a chance I'll have a look into the issue and submit a PR if I can work it out, but if you have any suggestions for where to start that would be helpful.