DOCBOOK-APPS: Bug report: contrib/imagemap/imagemap.dsl

If I am using contrib/imagemap/imagemap.dsl with an
<area> whose "linkid" is not valid, I get an error:

../html/dbhtml.dsl:28:23:E: 1st argument for primitive "number->string" of
wrong type: "#f" not a number

It looks like the call to (element-id) gets confused if the 
linkid doesn't exist.

What is the best way to make this problem go away?  Should this
be fixed in imagemap.dsl or dbhtml.dsl?  What is the best way
to fix it?

-k