Language Pack Upgrader: Check return value before accessing the first array key.

Prevents a fatal error when Language_Pack_Upgrader::bulk_upgrade() returns a WP_Error object.

fixes #29470.
Built from https://develop.svn.wordpress.org/trunk@29675


git-svn-id: http://core.svn.wordpress.org/trunk@29450 1a063a9b-81f0-0310-95a4-ce76da25c4cd
Plugin install: Make sure h3's clear floats to avoid layout problems.

props SergeyBiryukov.
fixes #29465.

Built from https://develop.svn.wordpress.org/trunk@29676


git-svn-id: http://core.svn.wordpress.org/trunk@29451 1a063a9b-81f0-0310-95a4-ce76da25c4cd