Flaw detected and fixed - I will make a 3.06b ASAP, 
check the website regurlarly, should be put tonight or 
tomorrow.

--- htslib.c    Sun Sep  9 19:29:28 2001
+++ htslib.c.new        Wed Sep 19 10:12:50 2001
@@ -2834,7 +2834,7 @@
     return concat(fil_noquery,"");
   }
   else
-    return NULL;
+    return "";
 }
 // known type?..
 //  0 : no