Package dropdowns break with empty namespace

[mcombuechen]

When dealing with packages without a namespace, the package selector dropdowns don't play nicely. For example, when dealing with package pkg:npm/acorn@7.4.1, it is impossible to ever get to the selection of the package and version since the empty namespace will keep the package name selector disabled.

Furthermore, the empty namespace will show up as a slightly smaller option due to the label being an empty string.

[mcombuechen]

The empty namespace renders as a UI bug in react-select:

[mcombuechen]

The package name selector remains disabled when the empty namespace was selected: