Merge lp://staging/~marcustomlinson/unity-scope-click/lp-1591422 into lp://staging/unity-scope-click

Looking at:

    https://errors.ubuntu.com/problem/f271ff40a203e6d22ab0bf36beb8f6f6adddb90a,

we can see that the crash originates from:

    ubuntuone_credentials.cpp:63 -> "promise.set_value(token);"

Digging a little deeper into the future source, _M_set_result() seems to only throw std::future_error for the promise_already_satisfied condition. This unhandled exception is tearing down the scope.

We have 2 places in code where getCredentials() is called:
    click::CredentialsService::getToken()
    & InstalledPreview::get_consumer_key()

I suspect that during "QCoreApplication::processEvents();" in click::CredentialsService::getToken(), we may risk processing 2 getCredentials() calls in parallel, causing multiple callbacks into the signal handler.

This change adds a safety net which may or may not make the issue go away completely, but it certainly shouldn't make things any worse.

The basics of this look sound, but would be nice if the statements were structured consistent with the rest of the code, like so:

try {
    promise.set_value();
} catch (const std::future_error&) {
    // Ignore promise_already_satisfied
}

> The basics of this look sound, but would be nice if the statements were
> structured consistent with the rest of the code, like so:
>
> try {
> promise.set_value();
> } catch (const std::future_error&) {
> // Ignore promise_already_satisfied
> }

Sure, done.