Handle config defaults better

[cpeel]

This is a set of small commits that better support the default (often null) configuration values set in SiteConfig. These are always set on TEST and PROD but new sites and test configurations don't necessarily need to set them and the default of null should work.

This is prep work to remove the bash-based configuration mechanism.

[bpfoley]

A question, about this... not strictly relevant to the patch, but still... why do we make $filename an argument? We only ever use pinc/site_vars.php and that's from the one callsite at the end of this file, right? Having require $filename; like this makes life more difficult on static analysers like PHPStan: they choke on the non-literal argument, and can't see the dependency.

[cpeel]

The thought was that for handling some of our upgrade checks it will make it easier to point to another config file to load the values within the script, effectively:

require_once(__DIR__ . "/../pinc/SiteConfig.inc");
SiteConfig::load($some_config_file);  // <-- overwrite the values from the new config file

I'm still finalizing that code now and if we don't actually need it I can rip the configurable-ness out.

[bpfoley]

A minor stylistic thing, but if you wanted to, you could fuse this with the assignment above: PHP scopes assignments within if conditions to the block containing the if.

if (($forum_id = ProjectStates::get_forum($this->state)) == null) {
    return null;
}

[cpeel]

If PHP is scoping the assignment to within the if() block then I don't want it here because it's used outside the if() scope, right? The other case in ProjcatTransition.inc I do.

[bpfoley]

Perhaps surprisingly, the scoping is the block that contains the if, not the the block with the 'then' body.

function foo() {
    if (($r = rand(0, 100)) > 50) {
       echo "$r is luckier than average!\n"; // <-- in scope here
    }
    echo "You rolled $r\n";  // <-- but also in scope here
}
foo();