LUCENE-5790: Fix compareTo in MutableValueDouble and MutableValueBool, this caused incorrect results when grouping on fields with missing values (merge r1608639)

git-svn-id: https://svn.apache.org/repos/asf/lucene/dev/branches/branch_4x@1608640 13f79535-47bb-0310-9956-ffa450edef68