a transistor's first tile record is a well or substrate type;
normally this is avoided, but if that's the only device terminal
that connects to the node, it will be used. Also changed the
code to not report a failure when space is found under the
device, when space is allowed as a substrate type. Instead it
will print a message that the substrate is not being extracted as
a resistive network. However, note that the correct solution is
to do what the regular "extract" code does, which is to paint the
substrate type in the cell area first, so that there are valid
tile types to use for extracting the substrate network.
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