Silent failure when layer_out_dims is not long enough to include middle modules

[jdunnmon]

This condition:

metal/metal/end_model/end_model.py

Line 102 in 7e3a838

if num_mid_layers == 0:

Causes the middle modules to just not be added. We should have a check here to either (a) make sure that the number of middle modules match up with the number specified or (b) at least print a statement to inform the user that we're ignoring their middle modules.