Fix Regression Bug in Mint Mate Sound Control

[ChrisJUK]

The Mint Mate 18.2, 18.3 control panel 'Sound Preferences' window 'Hardware' and 'input' tabs correctly show the different sound outputs/outputs (inbuilt analogue, HDMI, and USB sound bar), but the ''Output' tab only shows the inbuilt analogue.
As a result it is not possible to configure the HDMI or USB sound bar outputs.

Looking with terminal, the pacmd list-sinks command does show all 3 sinks (outputs) as present, and it is possible with pacmd to set the USB sound bar as the output.

Mint Mate 18, 18.1 both worked correctly, with the 'Output' tab showing the different sound outputs, and would configure the USB sound bar as the output.
Checking with live discs, Mint Cinnamon 18.3, KDE 18.3 and XFCE 18.3 all worked correctly.

Please can you fix this issue in Mint Mate 19.

Suggestion - if possible, put the Mint Cinnamon 'Sound Preferences' control window software into Mint Mate. The Cinnamon control is (IMHO) easier to understand and simpler to use.

Note - If the USB sound bar is turned with the sound system active (screen is locked, screen & usb sound bar turned off) then the output setting is reset to the inbuilt analogue output.