Fix directory ensurance until library fixed

SabreTools.DatTools/Statistics.cs

@@ -171,7 +171,7 @@ namespace SabreTools.DatTools
                 reportName = "report";
 
             // Get the proper output directory name
-            outDir = outDir?.Ensure();
+            outDir = (outDir ?? string.Empty).Ensure();
 
             InternalStopwatch watch = new($"Writing out report data to '{outDir}'");