Make plugin number of active installs consistent with plugin directory

[ovann86]

The WordPress Plugin Directory website and the WordPress Add Plugin search results are inconsistent with how they display the number of active installs when the count is low (e.g. less than 10).

In the WordPress Plugin Directory it displays 'Active Installs: Less than 10' and in WordPress it displays '0+ Active Installs'.

Search term to reproduce the search results is 'abn lookup'.

https://core.trac.wordpress.org/browser/trunk/src/wp-admin/includes/class-wp-plugin-install-list-table.php?marks=564-569&rev=38119#L561 needs an extra branch for 0 = 'Less than 10', assuming that is the logic that the Plugin Directory uses.

[ovann86]

Active Installs Count as seen in the WordPress Plugin Directory (Less than 10)

[ovann86]

Active Installs Count as seen in WordPress Add Plugins search results (0+ Active Installs)

[ocean90]

The same should be done here: https://core.trac.wordpress.org/browser/trunk/src/wp-admin/includes/plugin-install.php?rev=38119&marks=562-566#L561

[ovann86]

Add branches for 'Less Than 10' Active Installs - note using Title Case, as this is the standard used in this section - unlike in the WP Plugin Directory.

[ovann86]

Updated previous patch to use yoda conditions for new branches

[mitchelsliwa]

The patch applied and it successfully fixed the problem.

[dd32]

In 38729:

Plugins: Display 'Less Than 10' active installs of a plugin rather than '0+' active installs.

Props ovann86.
Fixes #37509.

[dd32]

I also switched out the !empty() to isset() to actually show Less than 10 on the plugin detail overview - previously this wasn't shown there when it was in that range.