duplicated code in TheoryInterferenceOverlay

[pixelzoom]

For code review #259, identified by grunt find-duplicates:

This code is duplicated in 2 places in TheoryInterferenceOverlay. Lines 63-79 and 86-101.

                  const separation = scene.slitSeparationProperty.value;
                  const arg = ( m + addition ) * scene.wavelength / separation;

                  if ( arg <= 1 ) {
                    const theta = sign * Math.asin( arg );

                    const x = LENGTH * Math.cos( theta );
                    const y = LENGTH * Math.sin( theta );
                    const line = new Line( barrierX, barrierY, barrierX + x, barrierY + y, {
                      stroke: type === 'maxima' ? MAXIMUM_COLOR : MINIMUM_COLOR,
                      lineWidth: LINE_WIDTH
                    } );
                    this.addChild( line );
                  }

[samreid]

Here's a visual diff:

The duplicated part is isolated to the if statement.

[samreid]

Factored out in preceding commit, please review.

[pixelzoom]

👍 Closing.