This application failed to start because it could not find or load the Qt platform plugin "xcb" in ""

[Walter Schwarzenfeld]

The recent update of the qt5* ports puzzled some things, could not 
update cause of qt5-networking is broken with__libressl. I reverted the 
partial update.

After this I got this error: This application failed to start because it 
could not find or load the Qt platform plugin "xcb" in "".

Problem withvlc and xpdf (maybe, with some more).  Vlc and xpdf 
core-dumps on start.

Does anybody know how to fix this?