Bug fix in PixelChargeCalibCondAlg (ATLASRECTS-4942)

The job is crashed when running valgrind.

This was happened in PixelChargeCalibCondAlg (ATLASRECTS-4942) that when the length of the array is less than 21.

Looking inside the contents in DB, actually, the contents itself seems buggy.

So far, in the code, when we meet less than 21 array size, we ignore this, since this should not be happened when the DB contents are correctly stored.

So, once the DB contents are fixed, this problem will be gone.