When g_option_context_parse fails, context and error variables are not getting free'd
which results in memory leaks. Free'ing the same.
And replacing g_error_free with g_clear_error, which checks if the error being passed
is not NULL and sets the variable to NULL on free'ing.
https://bugzilla.gnome.org/show_bug.cgi?id=753852
This reverts commit 40fe5dcc84.
Using an idle probe here is not ideal because we'll send an EOS event
from the application thread... which might block for quite some time.
Go back to a block probe.
Bases on test app in bug #614296. Doesn't work reliably yet,
leads to not-negotiated errors sooner or later, even when
it's the same element being re-plugged.
