Posts, Post Types: Display a more specific error message when an attachment...

Posts, Post Types: Display a more specific error message when an attachment could not be inserted into the database.

Props shital-patel, Presskopp, ocean90.
Fixes #50325.
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git-svn-id: https://core.svn.wordpress.org/trunk@47696 1a063a9b-81f0-0310-95a4-ce76da25c4cd