Updated QT stack fix security vulnerability

This update provides the 5.12.6 QT stack maintenance release and fixes the following security issue: An out-of-bounds memory access in the generateDirectionalRuns() function in qtextengine.cpp in Qt qtbase 5.11.x and 5.12.x before 5.12.5 allows attackers to cause a denial of service by crashing an application via a text file containing many directional characters (CVE-2019-18281). kwin and skrooge has been rebuilt to pick up proper dependencies on the updated QT packages.