decompose_uri() builtin throws errors on URIs with select parameters

URIs with odd query strings cause errors in reporter.log.

For example:

local something = decompose_uri("dfasjdfasdfasdf?asd");

results in:

error in /usr/local/bro-master/share/bro/base/utils/urls.bro, line 79: no such index (parts[1])

http://try.bro.org/#/trybro/saved/8505 demonstrates a pretty alright example.