Some BMP files have file size declared in the header equal to headers size

without image data, so try to correct that value before conducting checks on
declared file size.

Originally committed as revision 15924 to svn://svn.ffmpeg.org/ffmpeg/trunk

libavcodec/bmp.c

@@ -73,18 +73,22 @@ static int bmp_decode_frame(AVCodecContext *avctx,
     buf += 2; /* reserved2 */
 
     hsize = bytestream_get_le32(&buf); /* header size */
-    if(fsize <= hsize){
-        av_log(avctx, AV_LOG_ERROR, "declared file size is less than header size (%d < %d)\n",
-               fsize, hsize);
-        return -1;
-    }
-
     ihsize = bytestream_get_le32(&buf);       /* more header size */
     if(ihsize + 14 > hsize){
         av_log(avctx, AV_LOG_ERROR, "invalid header size %d\n", hsize);
         return -1;
     }
 
+    /* sometimes file size is set to some headers size, set a real size in that case */
+    if(fsize == 14 || fsize == ihsize + 14)
+        fsize = buf_size - 2;
+
+    if(fsize <= hsize){
+        av_log(avctx, AV_LOG_ERROR, "declared file size is less than header size (%d < %d)\n",
+               fsize, hsize);
+        return -1;
+    }
+
     switch(ihsize){
     case  40: // windib v3
     case  64: // OS/2 v2