Update handling of negative std.dev for feGaussianblur/feDropShadow

Source/core/svg/SVGFEGaussianBlurElement.cpp

Index: Source/core/svg/SVGFEGaussianBlurElement.cpp
diff --git a/Source/core/svg/SVGFEGaussianBlurElement.cpp b/Source/core/svg/SVGFEGaussianBlurElement.cpp
index c322d8dfd379d22cc1ca5fd6183bf7e28e4d1f6a..cfb1503edc502291f1c3ddb4485c5fb09b9acf3c 100644
--- a/Source/core/svg/SVGFEGaussianBlurElement.cpp
+++ b/Source/core/svg/SVGFEGaussianBlurElement.cpp
@@ -72,10 +72,14 @@ PassRefPtrWillBeRawPtr<FilterEffect> SVGFEGaussianBlurElement::build(SVGFilterBu
     if (!input1)
         return nullptr;
 
-    if (stdDeviationX()->currentValue()->value() < 0 || stdDeviationY()->currentValue()->value() < 0)
-        return nullptr;
-
-    RefPtrWillBeRawPtr<FilterEffect> effect = FEGaussianBlur::create(filter, stdDeviationX()->currentValue()->value(), stdDeviationY()->currentValue()->value());
+    // "A negative value or a value of zero disables the effect of the given
+    // filter primitive (i.e., the result is the filter input image)."
+    // (https://drafts.fxtf.org/filters/#element-attrdef-fegaussianblur-stddeviation)
+    //
+    // => Clamp to non-negative.
+    float stdDevX = std::max(0.0f, stdDeviationX()->currentValue()->value());
+    float stdDevY = std::max(0.0f, stdDeviationY()->currentValue()->value());
+    RefPtrWillBeRawPtr<FilterEffect> effect = FEGaussianBlur::create(filter, stdDevX, stdDevY);
     effect->inputEffects().append(input1);
     return effect.release();
 }