FIX: NullReferenceException when disabling actions.

Packages/com.unity.inputsystem/InputSystem/InputManager.cs

@@ -1342,12 +1342,15 @@ public void Remove(IInputStateChangeMonitor monitor, long monitorIndex)
                     return;
 
                 ////REVIEW: would be better to clean these up implicitly during the next traversal
-                for (var i = 0; i < listeners.Length; ++i)
+                for (var i = 0; i < signalled.length; ++i)
                     if (ReferenceEquals(listeners[i].monitor, monitor) && listeners[i].monitorIndex == monitorIndex)
                     {
-                        ArrayHelpers.EraseAt(ref listeners, i);
-                        ArrayHelpers.EraseAt(ref memoryRegions, i);
+                        var listenerCount = signalled.length;
+                        var memoryRegionCount = signalled.length;
+                        ArrayHelpers.EraseAtByMovingTail(listeners, ref listenerCount, i);
+                        ArrayHelpers.EraseAtByMovingTail(memoryRegions, ref memoryRegionCount, i);
                         signalled.SetLength(signalled.length - 1);
+                        break;
                     }
             }
 

Packages/com.unity.inputsystem/InputSystem/Utilities/ArrayHelpers.cs

@@ -328,9 +328,9 @@ public static bool Erase<TValue>(ref TValue[] array, TValue value)
         /// <summary>
         /// Erase an element from the array by moving the tail element into its place.
         /// </summary>
-        /// <param name="array"></param>
-        /// <param name="count"></param>
-        /// <param name="index"></param>
+        /// <param name="array">Array to modify. May be not <c>null</c>.</param>
+        /// <param name="count">Current number of elements inside of array. May be less than <c>array.Length</c>.</param>
+        /// <param name="index">Index of element to remove. Tail element will get moved into its place.</param>
         /// <typeparam name="TValue"></typeparam>
         /// <remarks>
         /// This method does not re-allocate the array. Instead <paramref name="count"/> is used
@@ -341,13 +341,15 @@ public static void EraseAtByMovingTail<TValue>(TValue[] array, ref int count, in
             Debug.Assert(array != null);
             Debug.Assert(index >= 0 && index < array.Length);
             Debug.Assert(count >= 0 && count <= array.Length);
+            Debug.Assert(index < count);
 
             // Move tail, if necessary.
             if (index != count - 1)
                 array[index] = array[count - 1];
 
             // Destroy current tail.
-            array[count - 1] = default(TValue);
+            if (count > 1)
+                array[count - 1] = default(TValue);
             --count;
         }