Only allow path as target for mpath

Source/core/svg/SVGMPathElement.cpp

Index: Source/core/svg/SVGMPathElement.cpp
diff --git a/Source/core/svg/SVGMPathElement.cpp b/Source/core/svg/SVGMPathElement.cpp
index 89d1a22632d177dc219468d0498215a475d57da9..f5e3e7abc7e8496d10a64cb4e1f4f37599ddb424 100644
--- a/Source/core/svg/SVGMPathElement.cpp
+++ b/Source/core/svg/SVGMPathElement.cpp
@@ -62,7 +62,7 @@ void SVGMPathElement::buildPendingResource()
             document().accessSVGExtensions().addPendingResource(id, this);
             ASSERT(hasPendingResources());
         }
-    } else if (target->isSVGElement()) {
+    } else if (isSVGPathElement(target)) {
         // Register us with the target in the dependencies map. Any change of hrefElement
         // that leads to relayout/repainting now informs us, so we can react to it.
         addReferenceTo(toSVGElement(target));