stream-manager: Ensure sending ducking changed signal even when unlinking sink-input...

stream-manager: Ensure sending ducking changed signal even when unlinking sink-input during ducking or unducking

Even though a sink-input affected by ducking DBus method is unlinking
in the middle of ducking or unducking process by ramp factor, the DBus
signal for ducking changed callback should be emitted properly.
This patch checks some conditions and emits the signal in that case.

[Version] 11.1.66
[Issue type] Improvement

Change-Id: Iab46f03af623f204ba351fa83941a2a03e77b4d3
Signed-off-by: Sangchul Lee <sc11.lee@samsung.com>