Fix mmap failed(2) on 32-bit FreeBSD (bb #2300).

off_t is 64-bit, size_t is still 32-bit and that causes unexpected integer
promotion here:
map_off = map->len - 2048

First the unsigned subtraction is performed, and then the unsigned (!) value
is sign-extended to 64-bit. Hence a negative value becomes positive, which is
wrong.

ChangeLog

@@ -1,3 +1,7 @@
+Tue Sep 28 12:42:01 EEST 2010 (edwin)
+-------------------------------------
+ * libclamav/pdf.c: fix mmap failed(2) on 32-bit FreeBSD (bb #2300).
+
 Thu Sep 23 17:59:26 CEST 2010 (acab)
 ------------------------------------
  * m4/acinclude: add alarm(10) to the CVE-2010-0405 check so we don't

libclamav/pdf.c

@@ -1024,7 +1024,7 @@ int cli_pdf(const char *dir, cli_ctx *ctx, off_t offset)
     offset += pdfver - start;
 
     /* find trailer and xref, don't fail if not found */
-    map_off = map->len - 2048;
+    map_off = (off_t)map->len - 2048;
     if (map_off < 0)
 	map_off = 0;
     bytesleft = map->len - map_off;