LinearRegressionModel uses only default parameters if yStd is 0

In the (rare) case when yStd is 0 in LinearRegression, parameters are not copied immediately to the created LinearRegressionModel instance. But they should (as in all other cases), because currently only the default column names are used in and returned by model.findSummaryModelAndPredictionCol(), which leads to schema validation errors.

The fix is two lines and should not be hard to check & apply.