avcodec/pgssubdec: Use av_fast_padded_malloc() for rle buffer

Fixes: use of uninitialized memeory
Fixes: msan_uninit-mem_7fa421d0e222_1765_Girl_With_The_Dragon_Tattoo_2_23_56.mkv
Found-by: Mateusz "j00ru" Jurczyk and Gynvael Coldwind
Signed-off-by: Michael Niedermayer <michaelni@gmx.at>

libavcodec/pgssubdec.c

@@ -232,7 +232,7 @@ static int parse_picture_segment(AVCodecContext *avctx,
     ctx->pictures[picture_id].w = width;
     ctx->pictures[picture_id].h = height;
 
-    av_fast_malloc(&ctx->pictures[picture_id].rle, &ctx->pictures[picture_id].rle_buffer_size, rle_bitmap_len);
+    av_fast_padded_malloc(&ctx->pictures[picture_id].rle, &ctx->pictures[picture_id].rle_buffer_size, rle_bitmap_len);
 
     if (!ctx->pictures[picture_id].rle)
         return -1;