pcx: Add missing padding to scanline buffer

Fixes out of array read

Found-by: Mateusz "j00ru" Jurczyk and Gynvael Coldwind
Signed-off-by: Michael Niedermayer <michaelni@gmx.at>

libavcodec/pcx.c

@@ -161,7 +161,7 @@ static int pcx_decode_frame(AVCodecContext *avctx, void *data, int *got_frame,
     ptr    = p->data[0];
     stride = p->linesize[0];
 
-    scanline = av_malloc(bytes_per_scanline);
+    scanline = av_malloc(bytes_per_scanline + FF_INPUT_BUFFER_PADDING_SIZE);
     if (!scanline)
         return AVERROR(ENOMEM);