Fix NLLanguageRecognizer crash (#6689)

The dispose of `nslang` was happening outside of the check if `nslang` is null. This was causing a crash when trying to recognise a string that contains just one number.

Fixes: #6688

src/NaturalLanguage/NLLanguageRecognizer.cs

@@ -33,11 +33,9 @@ public static NLLanguage GetDominantLanguage (string @string)
 		{
 			var nsstring = NSString.CreateNative (@string);
 			var nslang = _GetDominantLanguage (nsstring);
-			var lang =  NLLanguage.Undetermined;
-			if (nslang != null)
-				lang = NLLanguageExtensions.GetValue (nslang);
+			var lang = NLLanguageExtensions.GetValue (nslang);
+			nslang?.Dispose ();
 			NSString.ReleaseNative (nsstring);
-			nslang.Dispose ();
 			return lang;
 		}
 

tests/monotouch-test/NaturalLanguage/NLLanguageRecognizerTest.cs

@@ -55,5 +55,16 @@ public void Process ()
 				Assert.That (hypo.Count, Is.GreaterThan (0), "GetLanguageHypotheses");
 			}
 		}
+
+		[Test]
+		public void HandelNumbers()
+		{
+			using (var recognizer = new NLLanguageRecognizer ()) {
+				Assert.That (recognizer.DominantLanguage, Is.EqualTo (NLLanguage.Unevaluated), "DominantLanguage/Pre-Process");
+				var text = "2";
+				recognizer.Process (text);
+				Assert.That (recognizer.DominantLanguage, Is.EqualTo (NLLanguage.Unevaluated), "DominantLanguage/Post-Process");
+			}
+		}
 	}
 }