Unwrap the JoinHandle's result so we can match on its contents.

src/capi.rs

@@ -124,7 +124,7 @@ pub unsafe extern "C" fn mp4parse_read(context: *mut MediaContext, buffer: *cons
     // result in an Ok(..) otherwise, meaning we could see
     // Ok(Err(Error::..)) here. So map thread failures back
     // to an mp4parse::Error before converting to a C return value.
-    match task.join().or(Err(Error::AssertCaught)) {
+    match task.join().unwrap_or(Err(Error::AssertCaught)) {
         Ok(_) => MP4PARSE_OK,
         Err(Error::InvalidData) => MP4PARSE_ERROR_INVALID,
         Err(Error::Unsupported) => MP4PARSE_ERROR_UNSUPPORTED,