Treat standalone default/initial/inherit in font-family as invalid

Source/core/css/parser/CSSPropertyParser.cpp

Index: Source/core/css/parser/CSSPropertyParser.cpp
diff --git a/Source/core/css/parser/CSSPropertyParser.cpp b/Source/core/css/parser/CSSPropertyParser.cpp
index d99e0d96d7216fc0bffffc409e492f75c778380b..6dd294d5b18655ba75c3e2d3ff776487f844e9a3 100644
--- a/Source/core/css/parser/CSSPropertyParser.cpp
+++ b/Source/core/css/parser/CSSPropertyParser.cpp
@@ -4636,7 +4636,7 @@ PassRefPtrWillBeRawPtr<CSSValueList> CSSPropertyParser::parseFontFamily()
 
         if (isCSSWideKeyword(*value) && !inFamily) {
             if (nextValBreaksFont)
-                value = m_valueList->next();
+                return nullptr;
             else if (nextValIsFontName)
                 value = nextValue;
             continue;