House numbers, edge cases

Prevent initial values that are too large from causing an exception.
The largest value is 2^20 ie 1,048,576.

git-svn-id: http://svn.mkgmap.org.uk/mkgmap/trunk@2500 25d90789-57f7-4ee0-8453-03a3dfeeeb22
House numbers, edge cases

Abandon ranges that are greater than the max which is 2^17.

git-svn-id: http://svn.mkgmap.org.uk/mkgmap/trunk@2501 25d90789-57f7-4ee0-8453-03a3dfeeeb22