NetworkRequestDialog: Exit the dialog on connect failure

Connection failure (similar to connection success) is the end of the
processng of a request. We should dismiss the dialog on connection
failure.

Bug: 158844146
Bug: 158616070
Test: Manual tests - Simulate connection failure and ensure that the
dialog vanishes with a toast.

Change-Id: I625ca76298ed549dbed76d398aea0c957c9102fc
Merged-In: I625ca76298ed549dbed76d398aea0c957c9102fc