Cherry-pick 6d542b7. rdar://123016231

    AX: AccessibilitySVGElement::description() is missing several null-checks, causing crashes
    https://bugs.webkit.org/show_bug.cgi?id=269530
    rdar://123016231

    Reviewed by Chris Fleizach.

    * Source/WebCore/accessibility/AccessibilitySVGElement.cpp:
    (WebCore::AccessibilitySVGElement::description const):

    Canonical link: https://commits.webkit.org/274934@main

Identifier: 272448.786@safari-7618-branch

Source/WebCore/accessibility/AccessibilitySVGElement.cpp

@@ -138,26 +138,29 @@ String AccessibilitySVGElement::description() const
     if (!ariaDescription.isEmpty())
         return ariaDescription;
 
-    auto titleElements = childrenOfType<SVGTitleElement>(*element());
-    if (auto titleChild = childElementWithMatchingLanguage(titleElements))
-        return titleChild->textContent();
+    RefPtr element = this->element();
+    if (element) {
+        auto titleElements = childrenOfType<SVGTitleElement>(*element);
+        if (auto* titleChild = childElementWithMatchingLanguage(titleElements))
+            return titleChild->textContent();
+    }
 
-    if (is<SVGAElement>(element())) {
-        auto& xlinkTitle = element()->attributeWithoutSynchronization(XLinkNames::titleAttr);
+    if (is<SVGAElement>(element.get())) {
+        const auto& xlinkTitle = element->attributeWithoutSynchronization(XLinkNames::titleAttr);
         if (!xlinkTitle.isEmpty())
             return xlinkTitle;
     }
 
-    if (is<SVGUseElement>(element())) {
+    if (is<SVGUseElement>(element.get())) {
         if (auto* target = targetForUseElement())
             return target->description();
     }
 
     // FIXME: This is here to not break the svg-image.html test. But 'alt' is not
     // listed as a supported attribute of the 'image' element in the SVG spec:
     // https://www.w3.org/TR/SVG/struct.html#ImageElement
-    if (m_renderer->isRenderOrLegacyRenderSVGImage()) {
-        const AtomString& alt = getAttribute(HTMLNames::altAttr);
+    if (m_renderer && m_renderer->isRenderOrLegacyRenderSVGImage()) {
+        const auto& alt = getAttribute(HTMLNames::altAttr);
         if (!alt.isNull())
             return alt;
     }