Do not compare arrays against NULL (always true)

Fix cid #1048854

src/misc/fourcc.c

@@ -1463,7 +1463,7 @@ static entry_t Lookup( const staticentry_t p_list[], vlc_fourcc_t i_fourcc )
 
             memcpy( e.p_class, p_class, 4 );
             memcpy( e.p_fourcc, p->p_fourcc, 4 );
-            e.psz_description = p->psz_description ?
+            e.psz_description = p->psz_description[0] != '\0' ?
                                 p->psz_description : psz_description;
             break;
         }