give up on quad root if infinite

src/core/SkGeometry.cpp

Index: src/core/SkGeometry.cpp
diff --git a/src/core/SkGeometry.cpp b/src/core/SkGeometry.cpp
index f7c8f5736e64d0dc87fb83a749bd191b95909bf4..c25e18641a43bc0c766e1469a9c16d595e955282 100644
--- a/src/core/SkGeometry.cpp
+++ b/src/core/SkGeometry.cpp
@@ -90,7 +90,13 @@ int SkFindUnitQuadRoots(SkScalar A, SkScalar B, SkScalar C, SkScalar roots[2]) {
     SkScalar* r = roots;
 
     SkScalar R = B*B - 4*A*C;
-    if (R < 0 || SkScalarIsNaN(R)) {  // complex roots
+    if (R < 0 || !SkScalarIsFinite(R)) {  // complex roots
+        // if R is infinite, it's possible that it may still produce
+        // useful results if the operation was repeated in doubles
+        // the flipside is determining if the more precise answer
+        // isn't useful because surrounding machinery (e.g., subtracting
+        // the axis offset from C) already discards the extra precision
+        // more investigation and unit tests required...
         return 0;
     }
     R = SkScalarSqrt(R);