GitLab

Somehow a line "PreferredStyles =" is interpreted by QSettings
as a QStringList with a empty string.

Simply remove empty strings on reading the settings, as no
style can have that name.

Change-Id: If544e55f759c201d0621c71424a4ebedc8456d61
Task-number: QTCREATORBUG-15043
Reviewed-by: Orgad Shaneh <orgads@gmail.com>
Reviewed-by: Robert Loehning <robert.loehning@theqtcompany.com>