* API siteinfo query no longer throws an exception for empty sifilter parameter.

* API siteinfo query no longer throws an exception for empty sifilter parameter.

The parameter is defined as being one of two values ('local' or '!local'), but comes back as array() if it was specified but empty... which then got overly-strictly checked against 'false', which was used internally for the case where it's unspecified, and an exception thrown internally.

Now the filter parameter is nicely ignored whether it's unspecified or specified as empty, which is good clear behavior.

As before, other values return a standard API error about invalid values being passed.