fix panic if len is zero

sub/xpat/src/hexdump.rs

@@ -45,6 +45,12 @@ impl<'s, T: Scannable + ?Sized, R: RangeBounds<usize>> Display for HexDump<'s, T
             (start, end)
         };
 
+        // if there is nothing to print then just return...
+        // this also prevents the ilog below from crashing :)
+        if end == 0 || start > end {
+            return Ok(())
+        }
+
         // the number of digits the address column should have
         let digits = (end.ilog(16) as usize + 1).max(4);