A couple fixes for recording demonstrations (#1999)

* Sanitize demo filenames so that they can't be too long, overflow the header, and corrupt demo files
* Fix issue where 1st demo of each episode is always recorded as 0 action

UnitySDK/Assets/ML-Agents/Editor/Tests/DemonstrationTests.cs

         [Test]
         public void TestSanitization()
         {
-            const string dirtyString = "abc123&!@";
+            const string dirtyString = "abc1234567&!@";
-            var cleanString = DemonstrationRecorder.SanitizeName(dirtyString);
+            var cleanString = DemonstrationRecorder.SanitizeName(dirtyString, 6);
             Assert.AreNotEqual(dirtyString, cleanString);
             Assert.AreEqual(cleanString, knownCleanString);
         }

UnitySDK/Assets/ML-Agents/Scripts/Agent.cs

 
             BrainParameters param = brain.brainParameters;
             actionMasker = new ActionMasker(param);
-            if (param.vectorActionSpaceType == SpaceType.continuous)
+            // If we haven't initialized vectorActions, initialize to 0. This should only
+            // happen during the creation of the Agent. In subsequent episodes, vectorAction
+            // should stay the previous action before the Done(), so that it is properly recorded. 
+            if (action.vectorActions == null)
-                action.vectorActions = new float[param.vectorActionSize[0]];
-                info.storedVectorActions = new float[param.vectorActionSize[0]];
-            }
-            else
-            {
-                action.vectorActions = new float[param.vectorActionSize.Length];
-                info.storedVectorActions = new float[param.vectorActionSize.Length];
+                if (param.vectorActionSpaceType == SpaceType.continuous)
+                {
+                    action.vectorActions = new float[param.vectorActionSize[0]];
+                    info.storedVectorActions = new float[param.vectorActionSize[0]];
+                }
+                else
+                {
+                    action.vectorActions = new float[param.vectorActionSize.Length];
+                    info.storedVectorActions = new float[param.vectorActionSize.Length];
+                }
             }
 
             if (info.textObservation == null)

UnitySDK/Assets/ML-Agents/Scripts/DemonstrationRecorder.cs

         private Agent recordingAgent;
         private string filePath;
         private DemonstrationStore demoStore;
+        public const int MAX_NAME_LENGTH = 16;
 
         /// <summary>
         /// Initializes Demonstration store.
             {
                 recordingAgent = GetComponent<Agent>();
                 demoStore = new DemonstrationStore();
-                demonstrationName = SanitizeName(demonstrationName);
+                demonstrationName = SanitizeName(demonstrationName, MAX_NAME_LENGTH);
                 demoStore.Initialize(
                     demonstrationName, 
                     recordingAgent.brain.brainParameters, 
 
         /// <summary>
         /// Removes all characters except alphanumerics from demonstration name.
+        /// Shorten name if it is longer than the maxNameLength.
-        public static string SanitizeName(string demoName)
+        public static string SanitizeName(string demoName, int maxNameLength)
+            // If the string is too long, it will overflow the metadata. 
+            if (demoName.Length > maxNameLength)
+            {
+                demoName = demoName.Substring(0, maxNameLength);
+            }
             return demoName;
         }