Fix use of uninitialized value in SkSVGDevice

The asAGradient() function appears to be deprecated
(https://crbug.com/skia/8941) but there's no easy way to remove its use
here at the moment. So, fixing the surface-level issue.

Bug: oss-fuzz:23932
Change-Id: Ia9675f3b31644f2754421f27844e77c43f189c90
Reviewed-on: https://skia-review.googlesource.com/c/skia/+/300907
Reviewed-by: Florin Malita <fmalita@chromium.org>
Auto-Submit: Tyler Denniston <tdenniston@google.com>
Commit-Queue: Tyler Denniston <tdenniston@google.com>

Author: tdenniston

src/svg/SkSVGDevice.cpp

@@ -401,7 +401,7 @@ void SkSVGDevice::AutoElement::addGradientShaderResources(const SkShader* shader
                                                           const SkPaint& paint,
                                                           Resources* resources) {
     SkShader::GradientInfo grInfo;
-    grInfo.fColorCount = 0;
+    memset(&grInfo, 0, sizeof(grInfo));
     if (SkShader::kLinear_GradientType != shader->asAGradient(&grInfo)) {
         // TODO: non-linear gradient support
         return;