squashSpaces() return null for an empty string, as this seems to be the expected value in the calling routines

git-svn-id: http://svn.mkgmap.org.uk/mkgmap/trunk@2650 25d90789-57f7-4ee0-8453-03a3dfeeeb22
- add log message for invalid housenumbers
- handle case that java.util.regex.Pattern.split() can return an array with length 0



git-svn-id: http://svn.mkgmap.org.uk/mkgmap/trunk@2651 25d90789-57f7-4ee0-8453-03a3dfeeeb22