manweb: avoid null concatenation

dist/manweb

diff --git a/dist/manweb b/dist/manweb
index 32e9029..ce455da 100755
--- a/dist/manweb
+++ b/dist/manweb
@@ -32,6 +32,10 @@
 			echo '<tr height=1><td colspan=2 bgcolor=#cccccc>'
 			echo '<tr height=1><td>'
 		}
+		if(~ $#name 0)
+			name=XXX-name-$j-XXX
+		if(~ $#n 0)
+			n=XXX-n-$j-XXX
 		echo -n '<tr><td valign=top><a href="'$name'.html">'$name'('$n')</a><td>'
 		sed -n '
 		/SH *NAM/,/SH/{