backport: no document duplicates in quick open
backport: no document duplicates in quick open

backport commit 574f2f6b870efe8471751db45d43e62013c6e4b2

FIXED IN: 4.13

cmacq2/kate,hlamer/kate,cmacq2/kate,sandsmark/kate,DickJ/kate,DickJ/kate,hlamer/kate,hlamer/kate,sandsmark/kate,hlamer/kate,sandsmark/kate,hlamer/kate,hlamer/kate,hlamer/kate,jfmcarreira/kate,jfmcarreira/kate,cmacq2/kate,hlamer/kate,DickJ/kate,hlamer/kate,DickJ/kate,sandsmark/kate,hlamer/kate,jfmcarreira/kate