roq: fix excessive memory alloc

Fixes Ticket802
Bug found by: Oana Stratulat

Signed-off-by: Michael Niedermayer <michaelni@gmx.at>

libavformat/idroqdec.c

@@ -30,6 +30,7 @@
 #include "libavutil/intreadwrite.h"
 #include "avformat.h"
 #include "internal.h"
+#include "avio_internal.h"
 
 #define RoQ_MAGIC_NUMBER 0x1084
 #define RoQ_CHUNK_PREAMBLE_SIZE 8
@@ -125,6 +126,8 @@ static int roq_read_packet(AVFormatContext *s,
         if(chunk_size > INT_MAX)
             return AVERROR_INVALIDDATA;
 
+        chunk_size = ffio_limit(pb, chunk_size);
+
         switch (chunk_type) {
 
         case RoQ_INFO: