ash: Fix a crash when going back to the main uber-tray popup from the network popup.
ash: Fix a crash when going back to the main uber-tray popup from the network popup.

Going back to the main popup from the network popup causes the network popup to
get destroyed. So trying to access its internals afterwards causes a crash.
Return early to avoid this.

BUG=none
TEST=none

Review URL: https://chromiumcodereview.appspot.com/10406020

git-svn-id: de016e52bd170d2d4f2344f9bf92d50478b649e0@137681 0039d316-1c4b-4281-b951-d872f2087c98

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