gallium/util: fix pipe_debug_message macro to allow 0 args

Signed-off-by: Ilia Mirkin <imirkin@alum.mit.edu>
Reviewed-by: Brian Paul <brianp@vmware.com>
Tested-by: Brian Paul <brianp@vmware.com>

src/gallium/auxiliary/util/u_debug.h

@@ -270,7 +270,7 @@ void _debug_assert_fail(const char *expr,
    static unsigned id = 0; \
    _pipe_debug_message(cb, &id, \
                        PIPE_DEBUG_TYPE_ ## type, \
-                       fmt, __VA_ARGS__); \
+                       fmt, ##__VA_ARGS__); \
 } while (0)
 
 struct pipe_debug_callback;