C++ indenter: Be more careful when comparing states.

Task-number: QTCREATORBUG-1818

src/plugins/cpptools/cppcodeformatter.cpp

@@ -427,7 +427,8 @@ void CodeFormatter::updateStateUntil(const QTextBlock &endBlock)
             break;
         if (blockData.m_blockRevision != it.revision())
             break;
-        if (previousState != blockData.m_beginState)
+        if (previousState.isEmpty() || blockData.m_beginState.isEmpty()
+                || previousState != blockData.m_beginState)
             break;
         if (loadLexerState(it) == -1)
             break;