Use assertion for impossible case(The Predict() can ensure the token is…

Use assertion for impossible case(The Predict() can ensure the token is ColonToken, otherwise it would be marked as Error state. So there is no need to check ColonToken again).

include/rapidjson/reader.h

@@ -1273,12 +1273,9 @@ private:
                 return dst;
 
         case IterativeParsingKeyValueDelimiterState:
-            if (token == ColonToken) {
-                is.Take();
-                return dst;
-            }
-            else
-                return IterativeParsingErrorState;
+            RAPIDJSON_ASSERT(token == ColonToken);
+            is.Take();
+            return dst;
 
         case IterativeParsingMemberValueState:
             // Must be non-compound value. Or it would be ObjectInitial or ArrayInitial state.