Should still log a message even if AllowFailureWithoutError is set

[KirillOsenkov]

Looking at this logic:

msbuild/src/Build/BackEnd/Components/RequestBuilder/TaskBuilder.cs

Lines 937 to 958 in e9593e8

	// When a task fails it must log an error. If a task fails to do so,
	// that is logged as an error. MSBuild tasks are an exception because
	// errors are not logged directly from them, but the tasks spawned by them.
	IBuildEngine be = host.TaskInstance.BuildEngine;
	if (taskReturned && !taskResult && !taskLoggingContext.HasLoggedErrors && (be is TaskHost th ? th.BuildRequestsSucceeded : false) && (be is IBuildEngine7 be7 ? !be7.AllowFailureWithoutError : true))
	{
	if (_continueOnError == ContinueOnError.WarnAndContinue)
	{
	taskLoggingContext.LogWarning(null,
	new BuildEventFileInfo(_targetChildInstance.Location),
	"TaskReturnedFalseButDidNotLogError",
	_taskNode.Name);
	taskLoggingContext.LogComment(MessageImportance.Normal, "ErrorConvertedIntoWarning");
	}
	else
	{
	taskLoggingContext.LogError(new BuildEventFileInfo(_targetChildInstance.Location),
	"TaskReturnedFalseButDidNotLogError",
	_taskNode.Name);
	}
	}

we should still log a message if AllowFailureWithoutError is set. If it's set, currently we log nothing, and that's makes it impossible to debug. We should log a message instead of logging nothing at all.

See here microsoft/vstest#2953 for a real-world scenario where this would have helped a lot. VSTest sets AllowFailureWithoutError so we get ye olde

Build FAILED.
    0 Warning(s)
    0 Error(s)