Add prototype for handlefile, so that it is possible to call it before it
is defined.  Future compilers are likely not to accept implicit function
declarations by default.

Submitted upstream: <https://sourceforge.net/p/xbiso/patches/3/>

diff --git a/xbiso.c b/xbiso.c
index 6372944f7ec91120..c472c040d96e48a9 100644
--- a/xbiso.c
+++ b/xbiso.c
@@ -93,6 +93,7 @@ typedef off_t OFFT;
 typedef off64_t OFFT;
 #endif
 
+int handlefile(OFFT offset, int dtable);
 
 int main(int argc, char *argv[]) {
   char *dbuf,*fname;
@@ -269,6 +270,7 @@ int main(int argc, char *argv[]) {
   exit(0);
 }
 
+int
 handlefile(OFFT offset, int dtable) {
   TABLE dirent;