Minor change to the SimExternalConnection::read implementation.

Style

• All variable and function names make sense.
• The code is properly formatted (consider running git clang-format).

Performance

• All CPU-hot paths are well optimized.
• The proper containers are used (for example std::vector vs VectorRef).
• There are no new known SlowTask traces.

Testing

• The code was sufficiently tested in simulation.
• If there are new parameters or knobs, different values are tested in simulation.
• ASSERT, ASSERT_WE_THINK, and TEST macros are added in appropriate places.
• Unit tests were added for new algorithms and data structure that make sense to unit-test
• If this is a bugfix: there is a test that can easily reproduce the bug.