[Reland] Fix SkTwoPointConicalGradient zero-radius handling

src/effects/gradients/SkGradientShader.cpp

 /*
  * Copyright 2006 The Android Open Source Project
  *
  * Use of this source code is governed by a BSD-style license that can be
  * found in the LICENSE file.
  */
 
 #include "Sk4fLinearGradient.h"
 #include "SkGradientShaderPriv.h"
 #include "SkLinearGradient.h"
@@ skipping 822 matching lines @@
                                                   int colorCount,
                                                   SkShader::TileMode mode,
                                                   uint32_t flags,
                                                   const SkMatrix* localMatrix) {
     if (startRadius < 0 || endRadius < 0) {
         return nullptr;
     }
     if (!valid_grad(colors, pos, colorCount, mode)) {
         return nullptr;
     }
-    if (start == end && startRadius == endRadius) {
-        return SkShader::CreateEmptyShader();
+    if (startRadius == endRadius) {
+        if (start == end || startRadius == 0) {
+            return SkShader::CreateEmptyShader();
+        }
     }
 
     EXPAND_1_COLOR(colorCount);
 
     bool flipGradient = startRadius > endRadius;
 
     SkGradientShaderBase::Descriptor desc;
 
     if (!flipGradient) {
         desc_init(&desc, colors, pos, colorCount, mode, flags, localMatrix);
@@ skipping 349 matching lines @@
             (*stops)[i] = stop;
             stop = i < outColors - 1 ? stop + random->nextUScalar1() * (1.f - stop) : 1.f;
         }
     }
     *tm = static_cast<SkShader::TileMode>(random->nextULessThan(SkShader::kTileModeCount));
 
     return outColors;
 }
 
 #endif