Add additional protection against blank n-grams

MarkovGrams/NGrams.cs

@@ -94,6 +94,7 @@ namespace MarkovGrams
 				string[] parts = str.Split(" ".ToCharArray());
 				for (int i = 0; i < parts.Length - order; i++) {
 					string ngram = string.Join(" ", parts.Skip(i).Take(order)).Trim();
+					if (ngram.Trim().Length == 0) continue;
 					if (!results.ContainsKey(ngram))
 						results[ngram] = 0;
 					results[ngram]++;