resourceloader: Let wgResourceLoaderMaxQueryLength=-1 fallback to default

resourceloader: Let wgResourceLoaderMaxQueryLength=-1 fallback to default

Follows-up 3ac385a0c39a622c. This was generated by the installer at some
point and we've received two user reports of someone being caught by
this. We don't need to support "unlimited" anymore, but at least make it
do something more sensible, like using the default of 2000.

Previously, it was effectively treating the -1 like 0,
which was causing "debug mode"-like behaviour for end users.

Bug: T251789
Change-Id: I483d5312e6fa25a0b00bb6173ed01eeb99ad42aa
(cherry picked from commit fcd799ad54facda32aad127bbb4576fc2af078cc)