batch: return error if select into gets empty

[vagetablechicken]

OpenMLDB/java/openmldb-batch/src/main/scala/com/_4paradigm/openmldb/batch/nodes/SelectIntoPlan.scala

Lines 39 to 41 in 420398b

	if (input.getDf().isEmpty) {
	logger.info("select empty, skip save")
	} else {

If select closure in select into result is empty, we just skip saving, and the job is succeed. But users can't find the output file. It's not intuitive.
We should throw an exception.

[lumianph]

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#1344