av_tx_init: accept NULL scale for RDFT

Make av_tx_init() agree with documentation:

     * Real to complex and complex to real DFTs.
     * For the float and int32 variants, the scale type is 'float', while for
     * the double variant, it's a 'double'. If scale is NULL, 1.0 will be used
     * as a default.

Reviewed-by: Lynne <dev@lynne.ee>
Signed-off-by: Peter Ross <pross@xvid.org>

libavutil/tx.c

@@ -914,9 +914,9 @@ av_cold int av_tx_init(AVTXContext **ctx, av_tx_fn *tx, enum AVTXType type,
     if (!(flags & AV_TX_INPLACE))
         flags |= FF_TX_OUT_OF_PLACE;
 
-    if (!scale && ((type == AV_TX_FLOAT_MDCT) || (type == AV_TX_INT32_MDCT)))
+    if (!scale && ((type == AV_TX_FLOAT_MDCT) || (type == AV_TX_INT32_MDCT) || (type == AV_TX_FLOAT_RDFT) || (AV_TX_INT32_RDFT)))
         scale = &default_scale_f;
-    else if (!scale && (type == AV_TX_DOUBLE_MDCT))
+    else if (!scale && ((type == AV_TX_DOUBLE_MDCT) || (type == AV_TX_DOUBLE_RDFT)))
         scale = &default_scale_d;
 
     ret = ff_tx_init_subtx(&tmp, type, flags, NULL, len, inv, scale);