Get Tolk working again.

Two Tolk instances were being created. One checked for the presence of a screen reader. The other actually performed the speech, and was returned as part of the `TTS` instance.

Unfortunately, Tolk doesn't seem to appreciate being called twice. So here we check if a screen reader is detected and, if one is, return the instance that did the detection. Otherwise, error out and return the WinRT backend.

src/backends/tolk.rs

@@ -7,11 +7,14 @@ use crate::{Backend, Error, Features};
 pub struct Tolk(TolkPtr);
 
 impl Tolk {
-    pub fn new() -> Self {
+    pub fn new() -> Option<Self> {
         info!("Initializing Tolk backend");
         let tolk = TolkPtr::new();
-        tolk.try_sapi(true);
-        Tolk(tolk)
+        if tolk.detect_screen_reader().is_some() {
+            Some(Tolk(tolk))
+        } else {
+            None
+        }
     }
 }
 

src/lib.rs

@@ -93,7 +93,11 @@ impl TTS {
             #[cfg(windows)]
             Backends::Tolk => {
                 let tts = backends::Tolk::new();
+                if let Some(tts) = tts {
                     Ok(TTS(Box::new(tts)))
+                } else {
+                    Err(Error::NoneError)
+                }
             }
             #[cfg(windows)]
             Backends::WinRT => {
@@ -107,13 +111,10 @@ impl TTS {
         #[cfg(target_os = "linux")]
         let tts = TTS::new(Backends::SpeechDispatcher);
         #[cfg(windows)]
-        let tts = {
-            let tolk = tolk::Tolk::new();
-            if tolk.detect_screen_reader().is_some() {
-                TTS::new(Backends::Tolk)
+        let tts = if let Some(tts) = TTS::new(Backends::Tolk).ok() {
+            Ok(tts)
         } else {
             TTS::new(Backends::WinRT)
-            }
         };
         #[cfg(target_arch = "wasm32")]
         let tts = TTS::new(Backends::Web);