work around bug in kLineEdit

Summary:
a bug in kLineEdit causes spurious emission of textEdited signals when calling setText().

This in turn causes spurious calls of compilerEdited() when selecting a compiler in the compilers window,
which leads to a segfault (e.g. this bug https://bugs.kde.org/show_bug.cgi?id=373004) and I think some duplicates also.

I have submitted also a patch to kcompletion, https://phabricator.kde.org/D9808

This is a workaround for those systems until that is fixed

Reviewers: KDevelop, apol, mwolff

Reviewed By: KDevelop, mwolff

Subscribers: mwolff, anthonyfieroni, kdevelop-devel

Tags: KDevelop

Differential Revision: https://phabricator.kde.org/D9809
BUG: 373004
FIXED-IN: 5.2.2