When converting a location to an SMLoc, advance to the first...

    When converting a location to an SMLoc, advance to the first non-whitespace if the column is unknown(zero). This also fixes a small bug with call stack printing.

    Example:
    /tmp/file_C.py:21:5: error: 'foo.bar' op attribute 'something'
        raise app.UsageError('Too many command-line arguments.')
        ^
    /tmp/file_D.py:20:3: note: called from
      if len(argv) > 1:
      ^
    /tmp/file_E.py:19:1: note: called from
    def main(argv):
    ^
    /tmp/file_F.py:24:3: note: called from
      app.run(main)
      ^

--

PiperOrigin-RevId: 248151212