[Users] Mouse issue in editor window

[Ralf Mardorf]

The current official GTK related releases from upstream make Claws not
only look disgusting, but they at least cause one serious issue.

It's not always possible to position the cursor everywhere in the
editor's "Subject" area, when using the mouse. Using the
cursor/arrow-keys from the keyboard there's no issue.

claws-mail-git 3.13.2.r1.geb08800-1

Note the GTK related packages aren't from git, they are from
latest official releases from upstream.