qmljs: do not raise warning for yield statements

Task-number: QTCREATORBUG-21301
Change-Id: I2b358039f808faf8f979eb21410fa827cc132a57
Reviewed-by: Ulf Hermann <ulf.hermann@qt.io>

src/libs/qmljs/qmljscheck.cpp

@@ -1319,6 +1319,7 @@ bool Check::visit(ExpressionStatement *ast)
                 || cast<PreIncrementExpression *>(ast->expression)
                 || cast<PostIncrementExpression *>(ast->expression)
                 || cast<PostDecrementExpression *>(ast->expression)
+                || cast<YieldExpression *>(ast->expression)
                 || cast<FunctionExpression *>(ast->expression);
         if (BinaryExpression *binary = cast<BinaryExpression *>(ast->expression)) {
             switch (binary->op) {