SOLR-6383: RegexTransformer returns no results after replaceAll if regex does not match a value

git-svn-id: https://svn.apache.org/repos/asf/lucene/dev/trunk@1618488 13f79535-47bb-0310-9956-ffa450edef68
SOLR-2894: tweak test to workarround SOLR-6386

git-svn-id: https://svn.apache.org/repos/asf/lucene/dev/trunk@1618490 13f79535-47bb-0310-9956-ffa450edef68