Remove one direct _writeContext dependency (to allow better overriding)

Author: cowtowncoder

src/main/java/com/fasterxml/jackson/core/base/GeneratorBase.java

@@ -290,8 +290,8 @@ protected void _checkStdFeatureChanges(int newFeatureFlags, int changedFeatures)
     public void writeStartObject(Object forValue) throws IOException
     {
         writeStartObject();
-        if ((_writeContext != null) && (forValue != null)) {
-            _writeContext.setCurrentValue(forValue);
+        if (forValue != null) {
+            setCurrentValue(forValue);
         }
     }