Modifies syncer.replyChanRangeQuery method to use the LastBlockHeight
method on the query. LastBlockHeight safely calculates the ending
block height and prevents an overflow of start_block + num_blocks.
Prior to this change, query messages that had a start_block +
num_blocks that overflows uint32_max would return zero results in the
reply message.
Tests are added to fix the bug and ensure proper start and end values
are supplied to the channel graph filter.
