stop emitting warning about undefined variable $1 in the case of no leading text to trim from a line (i.e. $type is empty and there is no leading whitespace) (merged trunk r1528670)

git-svn-id: https://svn.apache.org/repos/asf/lucene/dev/branches/branch_4x@1528671 13f79535-47bb-0310-9956-ffa450edef68