Catch panics and C<->Rust boundary (#201)

* Catch panics in callbacks and mark callbacks as invalid.
* Mark callbacks as invalid if they return Quit.

Cargo.toml

@@ -8,7 +8,7 @@ license = "MIT"
 name = "jack"
 readme = "README.md"
 repository = "https://github.com/RustAudio/rust-jack"
-version = "0.12.0"
+version = "0.12.1"
 
 [dependencies]
 bitflags = "1"

src/client/async_client.rs

@@ -2,6 +2,7 @@ use jack_sys as j;
 use std::fmt;
 use std::fmt::Debug;
 use std::mem;
+use std::sync::atomic::AtomicBool;
 
 use super::callbacks::clear_callbacks;
 use super::callbacks::{CallbackContext, NotificationHandler, ProcessHandler};
@@ -58,6 +59,7 @@ where
                 client,
                 notification: notification_handler,
                 process: process_handler,
+                is_valid: AtomicBool::new(true),
             });
             CallbackContext::register_callbacks(&mut callback_context)?;
             sleep_on_test();