Update handling of negative std.dev for feGaussianblur/feDropShadow

Source/core/svg/SVGFEGaussianBlurElement.cpp

 /*
  * Copyright (C) 2004, 2005, 2007 Nikolas Zimmermann <zimmermann@kde.org>
  * Copyright (C) 2004, 2005, 2006 Rob Buis <buis@kde.org>
  *
  * This library is free software; you can redistribute it and/or
  * modify it under the terms of the GNU Library General Public
  * License as published by the Free Software Foundation; either
  * version 2 of the License, or (at your option) any later version.
  *
  * This library is distributed in the hope that it will be useful,
@@ skipping 54 matching lines @@
     SVGFilterPrimitiveStandardAttributes::svgAttributeChanged(attrName);
 }
 
 PassRefPtrWillBeRawPtr<FilterEffect> SVGFEGaussianBlurElement::build(SVGFilterBuilder* filterBuilder, Filter* filter)
 {
     FilterEffect* input1 = filterBuilder->getEffectById(AtomicString(m_in1->currentValue()->value()));
 
     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();
 }
 
 } // namespace blink