gstreamer/pad: Handle PadProbeReturn::Handled more correctly

If the probe returns Handled and the data was a Buffer we need to ensure
it was consumed. Queries need to be returned. The behavior of Handled
for other probes is not clear.

gstreamer/src/pad.rs

@@ -1080,8 +1080,31 @@ where
         flow_ret: from_glib((*info).ABI.abi.flow_ret),
     };
 
-    let ret = func(&Pad::from_glib_borrow(pad).unsafe_cast(), &mut probe_info).to_glib();
+    let ret = func(&Pad::from_glib_borrow(pad).unsafe_cast(), &mut probe_info);
 
+    if ret == PadProbeReturn::Handled {
+        // Handled queries need to be returned
+        // Handled buffers are consumed
+        // No other types can safely be used here
+
+        match probe_info.data {
+            Some(PadProbeData::Query(query)) => {
+                assert_eq!(data_type, Some(Query::static_type()));
+                (*info).data = query.as_mut_ptr() as *mut libc::c_void;
+            }
+            Some(PadProbeData::Buffer(_)) => {
+                assert_eq!(data_type, Some(Buffer::static_type()));
+                // Buffer not consumed by probe; consume it here
+            }
+            None if data_type == Some(Buffer::static_type()) => {
+                // Buffer consumed by probe
+            }
+            other => panic!(
+                "Bad data for {:?} pad probe returning Handled: {:?}",
+                data_type, other
+            ),
+        }
+    } else {
         match probe_info.data {
             Some(PadProbeData::Buffer(buffer)) => {
                 assert_eq!(data_type, Some(Buffer::static_type()));
@@ -1107,10 +1130,11 @@ where
                 assert_eq!(data_type, None);
             }
         }
+    }
 
     (*info).ABI.abi.flow_ret = probe_info.flow_ret.to_glib();
 
-    ret
+    ret.to_glib()
 }
 
 unsafe extern "C" fn trampoline_activate_function<