Do not consider title from non-css stylesheet for preferred set.

Source/core/dom/DocumentStyleSheetCollection.cpp

Index: Source/core/dom/DocumentStyleSheetCollection.cpp
diff --git a/Source/core/dom/DocumentStyleSheetCollection.cpp b/Source/core/dom/DocumentStyleSheetCollection.cpp
index ab2b1883a0caec33c166c0654cf5b1558a6f607e..f1b208e1a6bb3087cc2020aad485a21c9ab1534c 100644
--- a/Source/core/dom/DocumentStyleSheetCollection.cpp
+++ b/Source/core/dom/DocumentStyleSheetCollection.cpp
@@ -319,7 +319,7 @@ void DocumentStyleSheetCollection::collectActiveStyleSheets(Vector<RefPtr<StyleS
             // (thus making it PREFERRED or ALTERNATE rather than
             // PERSISTENT).
             AtomicString rel = e->getAttribute(relAttr);
-            if (!enabledViaScript && !title.isEmpty()) {
+            if (!enabledViaScript && sheet && !title.isEmpty()) {
                 // Yes, we have a title.
                 if (m_preferredStylesheetSetName.isEmpty()) {
                     // No preferred set has been established. If