only call scalar finite when necessary

src/pathops/SkPathOpsQuad.cpp

 /*
  * Copyright 2012 Google Inc.
  *
  * Use of this source code is governed by a BSD-style license that can be
  * found in the LICENSE file.
  */
 #include "SkIntersections.h"
 #include "SkLineParameters.h"
 #include "SkPathOpsCubic.h"
 #include "SkPathOpsCurve.h"
@@ skipping 101 matching lines @@
 Numeric Solutions (5.6) suggests to solve the quadratic by computing
        Q = -1/2(B + sgn(B)Sqrt(B^2 - 4 A C))
 and using the roots
       t1 = Q / A
       t2 = C / Q
 */
 // this does not discard real roots <= 0 or >= 1
 int SkDQuad::RootsReal(const double A, const double B, const double C, double s[2]) {
     const double p = B / (2 * A);
     const double q = C / A;
-    if (approximately_zero(A) && (approximately_zero_inverse(p) || approximately_zero_inverse(q))) {
+    if (!A || (approximately_zero(A) && (approximately_zero_inverse(p)
+            || approximately_zero_inverse(q)))) {
         if (approximately_zero(B)) {
             s[0] = 0;
             return C == 0;
         }
         s[0] = -C / B;
         return 1;
     }
     /* normal form: x^2 + px + q = 0 */
     const double p2 = p * p;
     if (!AlmostDequalUlps(p2, q) && p2 < q) {
@@ skipping 208 matching lines @@
  * c =             C
  */
 void SkDQuad::SetABC(const double* quad, double* a, double* b, double* c) {
     *a = quad[0];      // a = A
     *b = 2 * quad[2];  // b =     2*B
     *c = quad[4];      // c =             C
     *b -= *c;          // b =     2*B -   C
     *a -= *b;          // a = A - 2*B +   C
     *b -= *c;          // b =     2*B - 2*C
 }