Docs: Description is wrong in the return of network_domain_check()

[ishitaka]

Description is wrong in the return of network_domain_check()

current description is:

 * @return Whether a network exists.

must be:

 * @return string|false Base domain, or false if network does not exist.

[vaishalipanchal]

It looks like a good improvement, as suggested by @ishitaka, to explain the possible return values, that are currently either Base domain or false.

Here's are suggested adjustments for 45403.patch​:

* @return string|false Base domain if network exists, false otherwise.

[ishitaka]

@vaishalipanchal thanks for your suggestion.

[pento]

In 44460:

Docs: Improve the @return description of network_domain_check().

Props ishitaka, vaishalipanchal.
Fixes #45403.