CppTools: Fix formatting for lambdas with trailing return type

After the arrow, the state is still the same, as now a type is expected.
Only after the opening brace does the actual function start.

Fixes: QTCREATORBUG-18497
Change-Id: I7bf18fbd6907d36f8869af3a78ad617cf0ee9dbb
Reviewed-by: Christian Stenger <christian.stenger@qt.io>

tests/auto/cplusplus/codeformatter/tst_codeformatter.cpp

@@ -127,6 +127,7 @@ private Q_SLOTS:
     void strings();
     void initializerWithinFunctionArg();
     void shiftWithinInitializer();
+    void lambdaWithReturnType();
 };
 
 struct Line {
@@ -2196,6 +2197,18 @@ void tst_CodeFormatter::shiftWithinInitializer()
     checkIndent(data);
 }
 
+void tst_CodeFormatter::lambdaWithReturnType()
+{
+    QList<Line> data;
+    data << Line("int main() {")
+         << Line("    hello([]() -> void {")
+         << Line("        cout << \"world\";") // OK, same indentation/padding as above.
+         << Line("    });")
+         << Line("}")
+            ;
+    checkIndent(data);
+}
+
 QTEST_MAIN(tst_CodeFormatter)
 
 #include "tst_codeformatter.moc"