SAPI 4: Raise an exception during initialisation if no voices are detected

[jteh]

Currently, if a user has SAPI 4 installed but no SAPI 4 voices, the user can switch to SAPI 4 but will simply receive silence. It is then rather difficult to change back to a useable synth unless one knows the exact keystrokes.

Detecting SAPI 4 voices and hiding SAPI 4 if none are found would be nice, but is probably not viable due to the need to initialise SAPI 4 before this can be done. A more efficient option would be to raise an exception during initialisation if no SAPI 4 voices are found. This way, even though SAPI 4 will be included in the list of available synthesisers, a user cannot change to SAPI 4 if there are no voices.

[mdcurran]

This is no longer an issue as sapi4serotek and sapi4activeVoice are no longer in NVDA. The replacement sapi4 driver does now throw an exception if there are no available voices, and therefore allerts the user before changing synthesizers.