avcodec/iff: Reorder checks to avoid unnecessary alloc+free

Signed-off-by: Andreas Rheinhardt <andreas.rheinhardt@gmail.com>

libavcodec/iff.c

@@ -299,14 +299,13 @@ static int extract_header(AVCodecContext *const avctx,
                 avctx->pix_fmt = AV_PIX_FMT_RGB32;
                 av_freep(&s->mask_buf);
                 av_freep(&s->mask_palbuf);
-                s->mask_buf = av_malloc((s->planesize * 32) + AV_INPUT_BUFFER_PADDING_SIZE);
-                if (!s->mask_buf)
-                    return AVERROR(ENOMEM);
                 if (s->bpp > 16) {
                     av_log(avctx, AV_LOG_ERROR, "bpp %d too large for palette\n", s->bpp);
-                    av_freep(&s->mask_buf);
                     return AVERROR(ENOMEM);
                 }
+                s->mask_buf = av_malloc((s->planesize * 32) + AV_INPUT_BUFFER_PADDING_SIZE);
+                if (!s->mask_buf)
+                    return AVERROR(ENOMEM);
                 s->mask_palbuf = av_malloc((2 << s->bpp) * sizeof(uint32_t) + AV_INPUT_BUFFER_PADDING_SIZE);
                 if (!s->mask_palbuf) {
                     av_freep(&s->mask_buf);