AsyncLoop: Add test for zero-iteration loops

This mnemonically ensures that we'll remember to check for
these kinds of async loops.

include/asynchronousLoop.h

@@ -33,6 +33,11 @@ public:
 		return isComplete();
 	}
 
+	bool nTotalIsZero(void) const
+	{
+		return nTotal == 0;
+	}
+
 public:
 	const unsigned int nTotal;
 	std::atomic<unsigned int> nSucceeded, nFailed;

smocore/senseApis/senseApiManager.cpp

@@ -363,6 +363,12 @@ void SenseApiManager::attachAllSenseDevicesFromSpecsReq(
 	auto request = std::make_shared<AttachAllSenseDevicesFromSpecsReq>(
 		device::DeviceManager::deviceAttachmentSpecs.size(), std::move(cb));
 
+	if (request->loop.nTotalIsZero())
+	{
+		cb(request->loop);
+		return;
+	}
+
 	for (const auto& spec : device::DeviceManager::deviceAttachmentSpecs)
 	{
 		try {
@@ -421,6 +427,12 @@ void SenseApiManager::detachAllSenseDevicesReq(
 	auto request = std::make_shared<DetachAllSenseDevicesReq>(
 		device::DeviceManager::deviceAttachmentSpecs.size(), std::move(cb));
 
+	if (request->loop.nTotalIsZero())
+	{
+		cb(request->loop);
+		return;
+	}
+
 	for (const auto& spec : device::DeviceManager::deviceAttachmentSpecs)
 	{
 		try {