rtsp_server: RTSPServer::attach() is fallible

If we don't handle the case of RTSPServer::attach() failing, we end up
with a panic. Unfortunately, we don't get any details from the
underlying call so we've to live with a generic error. :(

examples/src/bin/rtsp-server-record.rs

@@ -130,7 +130,7 @@ fn main_loop() -> Result<(), Error> {
     // interested in them. In this example, we only do have one, so we can
     // leave the context parameter empty, it will automatically select
     // the default one.
-    let id = server.attach(None);
+    let id = server.attach(None)?;
 
     println!(
         "Stream ready at rtsps://127.0.0.1:{}/test",

examples/src/bin/rtsp-server-subclass.rs

@@ -58,7 +58,7 @@ fn main_loop() -> Result<(), Error> {
     // interested in them. In this example, we only do have one, so we can
     // leave the context parameter empty, it will automatically select
     // the default one.
-    let id = server.attach(None);
+    let id = server.attach(None)?;
 
     println!(
         "Stream ready at rtsp://127.0.0.1:{}/test",

examples/src/bin/rtsp-server.rs

@@ -66,7 +66,7 @@ fn main_loop() -> Result<(), Error> {
     // interested in them. In this example, we only do have one, so we can
     // leave the context parameter empty, it will automatically select
     // the default one.
-    let id = server.attach(None);
+    let id = server.attach(None)?;
 
     println!(
         "Stream ready at rtsp://127.0.0.1:{}/test",

gstreamer-rtsp-server/src/rtsp_server.rs

@@ -6,16 +6,27 @@ use glib::source::SourceId;
 use glib::translate::*;
 
 pub trait RTSPServerExtManual: 'static {
-    fn attach(&self, context: Option<&glib::MainContext>) -> SourceId;
+    fn attach(
+        &self,
+        context: Option<&glib::MainContext>,
+    ) -> Result<SourceId, glib::error::BoolError>;
 }
 
 impl<O: IsA<RTSPServer>> RTSPServerExtManual for O {
-    fn attach(&self, context: Option<&glib::MainContext>) -> SourceId {
+    fn attach(
+        &self,
+        context: Option<&glib::MainContext>,
+    ) -> Result<SourceId, glib::error::BoolError> {
         unsafe {
-            from_glib(ffi::gst_rtsp_server_attach(
+            match ffi::gst_rtsp_server_attach(
                 self.as_ref().to_glib_none().0,
                 context.to_glib_none().0,
-            ))
+            ) {
+                0 => Err(glib::bool_error!(
+                    "Failed to attach main context to RTSP server"
+                )),
+                id => Ok(from_glib(id)),
+            }
         }
     }
 }