workspacesView: Fix off-by-one error
This is basically 9f0e7632 (a.k.a. !1598 (merged)) ported over ed117090 (part of !1613 (merged)) which dropped this fix when copying things around.
The original explanation
The scroll adjustment's upper value corresponds to the number of workspaces, not to the last workspace index. We want the latter when mirroring the layout in RTL locales, so subtract 1.
Edited by Abderrahim Kitouni