Show users default namespaces after submit without namespaces
The first patch I189db67 for the story T189130 was incomplete and mostly
meant to quickly remove a blocker from the codebase. This patch here does:
- Remove all remaining hard coded "default to article/main namespace" instances.
- When the form is submitted with no namespaces selected, this empty array is intentionally not submitted as an URL parameter. This does have two effects:
- The users default namespaces become visible again. The code responsible for this is the same as when Special:Search is originally called with no URL parameters. This avoids having two code-paths for this.
- The URL contains less stuff. This magically solves parts of T188509.