well downhole plot misses first layer value if well head below layer centre

If a well head is below the commone layer centre but still above that particular column's surface block centre, it should have plot the value.

PyTOUGH and TIM uses separate codes, but both has bug in that they only uses the layer structure info, and did not take the column surface elevation into account.

TIM: _get_welltrack_blocks() need to consider column surface PyTOUGH: well_values() unrelated code, not used by TIM