[camera] Fix camera memory leak on IOS

[greggor01]

Needed to unregister the stream handler when disposing of the camera

Description

Per the flutter documentation, the stream handler should be unregistered using setStreamHandler with nil.
https://api.flutter.dev/objcdoc/Classes/FlutterEventChannel.html#/c:objc(cs)FlutterEventChannel(im)setStreamHandler:

Related Issues

Possibly fixes:
flutter/flutter#29586

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[greggor01]

Any news on when this might be incorporated? We have an app that will be posted in the app store very soon and it would be nice to have this fix included since it does indeed cause a crash on some IOS devices if the camera is opened and closed multiple times.

[mklim]

Thanks for your patience and the contribution! I have some feedback on the approach.

[mklim]

LGTM with one nit. Thanks again!

[JoseGeorges8]

Just tested the camera plugin version 0.5.2+2 on an iphone 5S running OS 12.3 and after every time the camera opens and closes the memory usage keeps on increasing quickly (took about 10 times for the camera to open and close to terminate the app)