ports-mgmt/portscout: Fix broken !SiteHandler logic

Fix a logic bug introduced in r401037, which caused ports without a
SiteHandler (GitHub, SourceForge, PyPI) not to be processed through the
fallback FTP or HTTP(S) cases.

I didn't pick this up in testing because only my ports were tested, most
of which use PyPI/GitHub, using the restrict maintainer setting in
portscout.conf.

[1] https://svnweb.freebsd.org/changeset/ports/401037

Pointyhat: koobs
Reported by: kwm (for mate, libdrm)
MFH: 2016Q1