avformat/siff: Fix checks and variable types

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

libavformat/siff.c

@@ -56,7 +56,7 @@ typedef struct SIFFContext {
     int curstrm;
     unsigned int pktsize;
     int gmcsize;
-    int sndsize;
+    unsigned int sndsize;
 
     unsigned int flags;
     uint8_t gmc[4];
@@ -208,10 +208,11 @@ static int siff_read_packet(AVFormatContext *s, AVPacket *pkt)
         }
 
         if (!c->curstrm) {
+            if (c->pktsize < 2LL + c->sndsize + c->gmcsize)
+                return AVERROR_INVALIDDATA;
+
             size = c->pktsize - c->sndsize - c->gmcsize - 2;
             size = ffio_limit(s->pb, size);
-            if (size < 0 || c->pktsize < c->sndsize)
-                return AVERROR_INVALIDDATA;
             if (av_new_packet(pkt, size + c->gmcsize + 2) < 0)
                 return AVERROR(ENOMEM);
             AV_WL16(pkt->data, c->flags);