fix(src,include,test): fixed multiple cases where a bad yaml was accepted.

Signed-off-by: Federico Di Pierro <nierro92@gmail.com>

src/scanner.h

@@ -177,6 +177,7 @@ class Scanner {
   // state info
   bool m_startedStream, m_endedStream;
   bool m_simpleKeyAllowed;
+  bool m_scalarValueAllowed;
   bool m_canBeJSONFlow;
   std::stack<SimpleKey> m_simpleKeys;
   std::stack<IndentMarker *> m_indents;