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;