macOS: Speak commands in control mode do not work

[sebwills]

1. In Preferences, Enable Control Mode, and, inside that, Speech functions
2. Write some text in Dasher, then zoom into the control node -> Speak -> All (or Para).

Expected: Dasher speaks the appropriate text
Actual: nothing happens

Note that the 'speak all on stop' and 'speak as you write' options do work.

Using master as of 2020-04-11.