Camera: Allow binder extension re-connection

Failing to establish a binder connection can leave the
connection manager in a state where the connection object
is valid but the corresponding proxy is absent.
Subsequent attempts to re-establish connection for the
same extension type will not succeed.
To avoid this, check for both valid connection
and proxy before skipping the connection sequence.

Flag: EXEMPT bugfix
Bug: 421012210
Test: Camera CTS

Change-Id: I5d5ff68c3aa2075a06c682b4b8abf8fd0201d2c9