lavc/tscc: Make 32bit output opaque.

Found-by: wm4

libavcodec/tscc.c

@@ -133,7 +133,7 @@ static av_cold int decode_init(AVCodecContext *avctx)
     case 24:
              avctx->pix_fmt = AV_PIX_FMT_BGR24;
              break;
-    case 32: avctx->pix_fmt = AV_PIX_FMT_RGB32; break;
+    case 32: avctx->pix_fmt = AV_PIX_FMT_0RGB32; break;
     default: av_log(avctx, AV_LOG_ERROR, "Camtasia error: unknown depth %i bpp\n", avctx->bits_per_coded_sample);
              return AVERROR_PATCHWELCOME;
     }