explicitly check for empty values when allowEmptyValues is false

[karenetheridge]

Mojo param parsing behaves as if allowEmptyValue is true, which is not the openapi default:

for my $pair (split /&/, $str) {
  next unless $pair =~ /^([^=]+)(?:=(.*))?$/;
  my ($name, $value) = ($1, $2 // '');
...

If we want to verify that empty values aren't passed, then we need to parse the parameters ourselves and error when $2 is undef.

[karenetheridge]

Just as in #63, this is difficult to do without having access to the original request (Mojo::Parameters::pairs turns a missing query value into '').

[karenetheridge]

allowEmptyValue recently saw some clarification in the spec: OAI/OpenAPI-Specification#3835

..which is reflected here via commit 061d164, which was released in v0.065.