Ensure the session singleton is NULLed out after disposal
Ensure the session singleton is NULLed out after disposal

If the session singleton pointer isn't set to NULL after the last
reference is decremented, the next constructor invocation won't create
a new session, but will try to get a reference to an old session which
only containse remaining garbage.

By adding the address of the singleton as a weak reference to the same
singleton, it is guaranteed that upon disposal, that weak pointer will
be set to NULL. This forces the next constructor to generate a session
all over.

RidgeRun/gstd-1.x,RidgeRun/gstd-1.x,RidgeRun/gstd-1.x,RidgeRun/gstd-1.x