Remove empty clock lines again

This effectively reverts 1cd21df.

Empty clock lines are not handled well by agenda's clockcheck as well as my own timetable tools.

init.el

@@ -1154,7 +1154,7 @@ accordingly."
                   org-clock-in-resume t
                   org-clock-into-drawer t
                   org-clock-idle-time nil
-                  org-clock-out-remove-zero-time-clocks nil
+                  org-clock-out-remove-zero-time-clocks t
                   org-clock-out-when-done '("DONE" "CANC" "MRGD" "WAIT" "HOLD")
                   org-clock-auto-clock-resolution 'when-no-clock-is-running
                   org-clock-mode-line-total 'auto
@@ -1266,7 +1266,7 @@ accordingly."
                         (org-deadline-past-days 0)
                         (org-agenda-sorting-strategy '(deadline-up priority-down))
                         (org-deadline-warning-days 30)))
-                      (tags-todo "TODO={CONT\\|ATTN}-HOLD-SOMEWHEN|PRIORITY=\"A\"+TODO<>\"\"-HOLD-SOMEWHEN"
+                      (tags-todo "TODO={CONT\\|ATTN}-HOLD-SOMEWHEN|PRIORITY=\"A\"+TODO<>\"\"-HOLD-SOMEWHEN-DATE"
                                  ((org-agenda-overriding-header "Things to do next (tasks with high priority or already started)")
                                   (org-agenda-todo-ignore-scheduled 'all)
                                   (org-agenda-todo-ignore-timestamp 0)