Avoid confusing error with pins on only one side
Avoid confusing error with pins on only one side

Previously if an IC schematic symbol only had pins on one side,
build_lib_ic.py would fail to index producing a confusing error.  This
change intercepts this problem and produces a more helpful error.

JMW95/agg-kicad,adamgreig/agg-kicad,JMW95/agg-kicad,adamgreig/agg-kicad