[CONFIGURATION-582] Fixed a StringIndexOutOfBoundsException.

Lines in properties files containing only whitespace are now handled
correctly when extracting comments.

git-svn-id: https://svn.apache.org/repos/asf/commons/proper/configuration/trunk@1623873 13f79535-47bb-0310-9956-ffa450edef68
[CONFIGURATION-582] Updated changes.xml.

git-svn-id: https://svn.apache.org/repos/asf/commons/proper/configuration/trunk@1623874 13f79535-47bb-0310-9956-ffa450edef68