[xml] Problem validating documents containing public entities with empty URIs

[Nikolai Weibull <now bitwi se>]

Hi!

Given the following files, invoking xmllint failes to validate a.xml,
instead spewing out the same couple of error messages over and over
again:

XML_CATALOG_FILES=catalog xmllint --valid a.xml

a.dtd:

<!ELEMENT a (b)>
<!ELEMENT b EMPTY>

a.xml:

<!DOCTYPE a PUBLIC "" "a.dtd" [
<!ENTITY b PUBLIC "b" "">
]>
<a>&b;</a>

b.ent:

<b/>

catalog:

<?xml version="1.0"?>
<!DOCTYPE catalog PUBLIC "-//OASIS//DTD Entity Resolution XML Catalog V1.0//EN"
  "http://www.oasis-open.org/committees/entity/release/1.0/catalog.dtd";>
<catalog xmlns="urn:oasis:names:tc:entity:xmlns:xml:catalog">
  <public publicId="b" uri="b.ent"/>
</catalog>

If, however, we modify a.xml by having something â anything â as the
URI to the public entity b, xmllint validates it without issues:

<!DOCTYPE a PUBLIC "" "a.dtd" [
<!ENTITY b PUBLIC "b" "N/A">
]>
<a>&b;</a>

I failed to determine a way of solving this, though I only glanced at
the source.