Fix https://issues.apache.org/bugzilla/show_bug.cgi?id=56529
Merged r1595289 from tomcat/trunk:
Review of r1595174:
1. Call iterator() once. It creates an object, so it is better do not waste such calls.
2. Style issues:
- "" does not make sense as 'generic' default for textAttributeValue. It makes sense for this specific case only.
- 3 spaces indent -> 4 spaces

git-svn-id: https://svn.apache.org/repos/asf/tomcat/tc7.0.x/trunk@1595366 13f79535-47bb-0310-9956-ffa450edef68
Fix https://issues.apache.org/bugzilla/show_bug.cgi?id=56529
Test case for attributes with empty string values in custom tags.
It is backport of r1595230 r1595365 from tomcat/trunk.

git-svn-id: https://svn.apache.org/repos/asf/tomcat/tc7.0.x/trunk@1595367 13f79535-47bb-0310-9956-ffa450edef68