detect: don't rescan when just distance is used

detect: don't rescan when just distance is used

Content inspection optimization: when just distance is used without
within we don't need to search recursively.

E.g. content:"a"; content:"b"; distance:1; will scan the buffer for
'a' and when it finds 'a' it will scan the remainder for 'b'. Until
now, the failure to find 'b' would lead to looking for the next 'a'
and then for 'b' after that. However, we already inspected the
entire buffer for 'b', so we know this will fail.