Fix missing spell check bar

Summary:

• the spell check bar removes itself from the bottom view bar, now is added again when required

BUG: 359682

Test Plan:

• write a text with spelling errors
• run the spell check, ignore errors
• run the spell check again, with the bar widget correctly showing up now

Reviewers: KTextEditor, dhaumann

Reviewed By: KTextEditor, dhaumann

Subscribers: dhaumann, Frameworks

Tags: Kate, Frameworks

Differential Revision: https://phabricator.kde.org/D8148