pcx: round up in bits->bytes conversion in a buffer size check

Fixes invalid reads.
Found-by: Mateusz "j00ru" Jurczyk and Gynvael Coldwind
CC:libav-stable@libav.org

libavcodec/pcx.c

@@ -109,7 +109,7 @@ static int pcx_decode_frame(AVCodecContext *avctx, void *data, int *got_frame,
     nplanes            = buf[65];
     bytes_per_scanline = nplanes * bytes_per_line;
 
-    if (bytes_per_scanline < w * bits_per_pixel * nplanes / 8 ||
+    if (bytes_per_scanline < (w * bits_per_pixel * nplanes + 7) / 8 ||
         (!compressed && bytes_per_scanline > buf_size / h)) {
         av_log(avctx, AV_LOG_ERROR, "PCX data is corrupted\n");
         return AVERROR_INVALIDDATA;