nvda

a8e8db19 - Ensure that no reference is kept to sapi4 synth on terminate (PR #10078)

Ensure that no reference is kept to sapi4 synth on terminate (PR #10078) When switching from SAPI4 to another synth, a reference to the sapi4 object is kept alive by a circular reference on the com Sink. Modified the design of both SAPI4 and 5 to clarify the use of weakRefs