telepathy: Call continuations in idle callbacks rather than directly

telepathy: Call continuations in idle callbacks rather than directly

The continuations will proceed to a g_simple_async_result_complete() call,
rather than a g_simple_async_result_complete_in_idle() call as I expected
(and didn’t check). This could result in the first continuation executing
a lot of code and starving the other continuations (and the original
prepare() call). By delaying the continuations to the idle queue, the
original prepare() call is guaranteed to finish first. Then the
continuations can only starve each other.

See: https://bugzilla.gnome.org/show_bug.cgi?id=677633