drop inputFocus on internalKeep

unmapping would do the same, but does not take
place to keep the window alive for the compositor
this breaks re-activation which takes place on
inputFocus events which won't occur since the
window got deactivated, but never lost the focus

BUG: 317484
FIXED-IN: 4.11
REVIEW: 111046

client.cpp

@@ -1183,6 +1183,8 @@ void Client::internalKeep()
     if (old == Unmapped || old == Withdrawn)
         map();
     m_decoInputExtent.unmap();
+    if (isActive())
+        workspace()->focusToNull(); // get rid of input focus, bug #317484
     updateHiddenPreview();
     addWorkspaceRepaint(visibleRect());
     workspace()->clientHidden(this);