fix a seg fault when fd does not exist

git-svn-id: file:///home/svn/mapi/trunk@800 8d5bb341-7cf1-0310-8cf6-ba355fef3186

src/common/fhelp.c

@@ -66,6 +66,10 @@ mapidflib_function_instance_t* fhlp_get_function_instance(global_function_list_t
      mapidflib_function_t *i;
 
      f=flist_get(gfl->fflist,fd);
+
+	if (!f)
+		return(NULL);
+     
      i=flist_get(f->flist,fid);