plotResiduals outlier colors black if test is not significant

[melina-leite]

Created to fix #451

Problem

Now, plotResiduals fails when using a nonDHARMa (and not a model) object for the simulationOutput argument.

Possible causes

Although, plotResiduals could work with nonDHARMa objects (using ensureDHARMa(convert = TRUE), testOutliers needs a DHARMa OR a model object (ensureDHARMa(convert = "Model") ).

So, when I test outliers to choose the color of the outliers in the plot, it throws an error. See example below:

testData = createData(sampleSize = 100, overdispersion = 0,
                      randomEffectVariance = 0)
fittedModel <- glm(observedResponse ~ Environment1 ,
                   family = "poisson", data = testData)
simulationOutput <- simulateResiduals(fittedModel = fittedModel, n = 50)

plotResiduals(simulationOutput)

plotResiduals(simulationOutput$scaledResiduals, form =
                simulationOutput$fittedPredictedResponse)