Fix vlc_pgettext

(cherry picked from commit 3f573875)

include/vlc_common.h

@@ -856,10 +856,13 @@ VLC_EXPORT( void *, vlc_memset, ( void *, int, size_t ) );
  *****************************************************************************/
 VLC_EXPORT( char *, vlc_gettext, ( const char *msgid ) LIBVLC_FORMAT_ARG(1) );
 
+#define vlc_pgettext( ctx, id ) \
+        vlc_pgettext_aux( ctx "\004" id, id )
+
 LIBVLC_FORMAT_ARG(2)
-static inline const char *vlc_pgettext( const char *ctx, const char *id )
+static inline const char *vlc_pgettext_aux( const char *ctx, const char *id )
 {
-    const char *tr = vlc_gettext( id );
+    const char *tr = vlc_gettext( ctx );
     return (tr == ctx) ? id : tr;
 }