Don't explode when location.hash == "#/123"

When location.hash is "#/123", section.js / jQuery errored with 
  "Error: Syntax error, unrecognized expression: .content[data-slug=/123]".
This fixes that.
Merge pull request #1596 from ahx/4.0-wip-fix-section-location-hash

Don't explode when location.hash == "#/123"