Make Element::attributes() less error-prone and simplify call sites

Source/core/editing/MarkupAccumulator.cpp

Index: Source/core/editing/MarkupAccumulator.cpp
diff --git a/Source/core/editing/MarkupAccumulator.cpp b/Source/core/editing/MarkupAccumulator.cpp
index ee12e50793c8ae2eeafab5f96e49e20ab5904795..6e73abca81069dd1505c50571a2b6f1418470808 100644
--- a/Source/core/editing/MarkupAccumulator.cpp
+++ b/Source/core/editing/MarkupAccumulator.cpp
@@ -385,12 +385,10 @@ void MarkupAccumulator::appendElement(StringBuilder& result, Element& element, N
 {
     appendOpenTag(result, element, namespaces);
 
-    if (element.hasAttributes()) {
-        AttributeCollection attributes = element.attributes();
-        AttributeCollection::const_iterator end = attributes.end();
-        for (AttributeCollection::const_iterator it = attributes.begin(); it != end; ++it)
-            appendAttribute(result, element, *it, namespaces);
-    }
+    AttributeCollection attributes = element.attributes();
+    AttributeCollection::const_iterator end = attributes.end();
+    for (AttributeCollection::const_iterator it = attributes.begin(); it != end; ++it)
+        appendAttribute(result, element, *it, namespaces);
 
     // Give an opportunity to subclasses to add their own attributes.
     appendCustomAttributes(result, element, namespaces);