pbutils: Manually implement DiscovererStreamInfo::stream_id()

It can return `NULL` in some cases. The next release will use an
`Option` but to keep backwards compatibility here, `NULL` is mapped to
the empty string for now.

Part-of: <https://gitlab.freedesktop.org/gstreamer/gstreamer-rs/-/merge_requests/1274>

gstreamer-pbutils/Gir.toml

@@ -279,6 +279,10 @@ final_type = false
     name = "list_free"
     ignore = true
 
+    [[object.function]]
+    name = "get_stream_id"
+    manual = true
+
 [[object]]
 name = "GstPbutils.DiscovererSubtitleInfo"
 status = "generate"

gstreamer-pbutils/src/auto/discoverer_stream_info.rs

@@ -40,10 +40,6 @@ pub trait DiscovererStreamInfoExt: 'static {
     #[must_use]
     fn previous(&self) -> Option<DiscovererStreamInfo>;
 
-    #[doc(alias = "gst_discoverer_stream_info_get_stream_id")]
-    #[doc(alias = "get_stream_id")]
-    fn stream_id(&self) -> glib::GString;
-
     #[cfg(any(feature = "v1_20", feature = "dox"))]
     #[cfg_attr(feature = "dox", doc(cfg(feature = "v1_20")))]
     #[doc(alias = "gst_discoverer_stream_info_get_stream_number")]
@@ -96,14 +92,6 @@ impl<O: IsA<DiscovererStreamInfo>> DiscovererStreamInfoExt for O {
         }
     }
 
-    fn stream_id(&self) -> glib::GString {
-        unsafe {
-            from_glib_none(ffi::gst_discoverer_stream_info_get_stream_id(
-                self.as_ref().to_glib_none().0,
-            ))
-        }
-    }
-
     #[cfg(any(feature = "v1_20", feature = "dox"))]
     #[cfg_attr(feature = "dox", doc(cfg(feature = "v1_20")))]
     fn stream_number(&self) -> i32 {

gstreamer-pbutils/src/discoverer_stream_info.rs

@@ -1,5 +1,7 @@
 // Take a look at the license at the top of the repository in the LICENSE file.
 
+use glib::translate::*;
+
 use crate::{prelude::*, DiscovererStreamInfo};
 
 #[derive(Debug)]
@@ -42,6 +44,18 @@ impl DiscovererStreamInfo {
             direction_forward: false,
         }
     }
+
+    fn stream_id(&self) -> glib::GString {
+        unsafe {
+            let ptr = ffi::gst_discoverer_stream_info_get_stream_id(self.as_ref().to_glib_none().0);
+
+            if ptr.is_null() {
+                glib::GString::new()
+            } else {
+                from_glib_none(ptr)
+            }
+        }
+    }
 }
 
 impl std::iter::FusedIterator for Iter {}