Change never-reachable code from assignmen to return (one more fix for …

…#121)

src/main/java/com/ctc/wstx/dtd/FullDTDReader.java

@@ -2769,7 +2769,7 @@ private void handleAttrDecl(DTDElement elem, char c, int index,
                 throwDTDAttrError("Unrecognized attribute default value directive #"+defTypeStr
                                    +ErrorConsts.ERR_DTD_DEFAULT_TYPE,
                                    elem, attrName);
-                defVal = null; // never gets here...
+                return; // never gets here...
             }
         } else {
             defVal = DefaultAttrValue.constructOptional();