If you want a task furter up in the QMC chain to not run when a QVD is found to be empty, let your script crash if you detect no loaded rows. I often use a self-invented statement called CRASH; to do this , because QlikView doesn't supply something similar. Your script then becomes
LOAD * FROM SomeFile (SomeOptions);
IF NoOfRows('TableSomething') = 0 THEN
Of course, the task will fail and you will get an appropriate email scream from the QDS. But the second task will not run.