MediaClient: IDs should be signed integers

* It's very important to use a negative value to identify
non valid or uninitialized connections. Additionally, it's preferred
to don't interfere with media_kit types as long as the framework use
it in the backend.

headers/private/media/experimental/MediaClientDefs.h

@@ -13,10 +13,11 @@
 namespace BPrivate { namespace media {
 
 
-typedef uint64 media_client_id;
+typedef int64 media_client_id;
+typedef int64 media_connection_id;
+
 typedef uint64 media_client_kinds;
 typedef uint64 media_connection_kinds;
-typedef uint64 media_connection_id;
 
 
 enum media_client_kind {