Add unittest for state transition to IterativeParsingMemberKeyState.

test/unittest/readertest.cpp

@@ -1041,6 +1041,7 @@ TEST(Reader, IterativeParsing_ErrorHandling) {
     TESTERRORHANDLING("{\"a\"}", kParseErrorObjectMissColon, 4u);
     TESTERRORHANDLING("{\"a\": 1", kParseErrorObjectMissCommaOrCurlyBracket, 7u);
     TESTERRORHANDLING("[1 2 3]", kParseErrorArrayMissCommaOrSquareBracket, 3u);
+    TESTERRORHANDLING("{\"a: 1", kParseErrorStringMissQuotationMark, 5u);
 
     // Any JSON value can be a valid root element in RFC7159.
     TESTERRORHANDLING("\"ab", kParseErrorStringMissQuotationMark, 2u);