Content hub/gallery crashes with content hub API

[Víctor R. Ruiz]

Problem related to this fix (tested with this silo): https://bugs.launchpad.net/unity-webapps-qml/+bug/1398916

Test case.
- Download lp:~webapps/unity-webapps-qml/trunk/
- adb shell mkdir www
- adb push trunk/examples/api-bindings/content-hub/www/ /home/phablet/www/
- phablet-shell
- ubuntu-html5-app-launcher --www=. --desktop_file_hint=/usr/share/applications/unitywebappsqmllauncher.desktop
- Tap on the Camera item from the peer list.
- Tap button to import content from the camera.
- After the camera opens, switch back to the webapp.
- Repeat a few times.

Expected result.
- No crashes.

Actual result.
- Eventually, content hub or camera crash do happen. Check /var/crash/

current build number: 253 + silo 13 (fix for bug #1398916).
device name: krillin
channel: ubuntu-touch/ubuntu-rtm/14.09-proposed