Minor: _ClipFinite() Prevent the propagation of undefined.

[martinfrances107]

This is a minor cosmetic change.

When the following code is ported into a language which detects and the rejects the propagation of undefined values form variable to variable.. I see this is happening in our java script code.

Looking at the code below as it flows into the for loop and into the complex branch of if statements I see e1 can be read before it is set. ( I have edited the line with a comment )

and when I run one of the standard tests -- using a debugger. I see the subsequent line

if (e0 && e1 ) {}

being computed as

if (undefined && 8 ) {}

this works ok because the natural initial value for e1 is actually 0b0000

Anyway this "read before write error" should be removed as it is a maintenance hazard.

    let e0, e1;
    for (let j = 0; j < n; j += 2) {
      x0 = x1, y0 = y1, x1 = points[j], y1 = points[j + 1];
      c0 = c1, c1 = this._regioncode(x1, y1);
      if (c0 === 0 && c1 === 0) {
        e0 = e1, e1 = 0;
        if (P) P.push(x1, y1);
        else P = [x1, y1];
      } else {
        let S, sx0, sy0, sx1, sy1;
        if (c0 === 0) {
          if ((S = this._clipSegment(x0, y0, x1, y1, c0, c1)) === null) continue;
          [sx0, sy0, sx1, sy1] = S;
        } else {
          if ((S = this._clipSegment(x1, y1, x0, y0, c1, c0)) === null) continue;
          [sx1, sy1, sx0, sy0] = S;
          e0 = e1, e1 = this._edgecode(sx0, sy0);  // e0 = e1 --- propagation of undefined happens here.
          if (e0 && e1) this._edge(i, e0, e1, P, P.length);
          if (P) P.push(sx0, sy0);
          else P = [sx0, sy0];
        }
        e0 = e1, e1 = this._edgecode(sx1, sy1);
        if (e0 && e1) this._edge(i, e0, e1, P, P.length);
        if (P) P.push(sx1, sy1);
        else P = [sx1, sy1];
      }
    }

[mbostock]

Merged as 6c69c725991308e71967e1fd776c25c7790e12bc. Thank you!