Rename ThrowIfDisposed to EnsureOpen

Author: paulirwin

src/Lucene.Net.Tests/Store/TestUnsafeChunkIndexInput.cs

@@ -169,7 +169,7 @@ internal ManagedChunkIndexInput(string desc, bool ownsRegion, ManagedChunkRegion
 
             public override object Clone()
             {
-                ThrowIfDisposed();
+                EnsureOpen();
                 var clone = (ManagedChunkIndexInput)base.Clone();
                 clone.isRoot = false;
                 clone.ResetClonedCursor();

src/Lucene.Net/Store/MMapDirectory.cs

@@ -370,7 +370,7 @@ internal MMapIndexInput(string resourceDescription,
             public override object Clone()
             {
                 // A disposed input must not hand out a working clone.
-                ThrowIfDisposed();
+                EnsureOpen();
                 // The clone shares the parent's SharedMapping but does NOT own it.
                 // ResetClonedCursor clears the inherited cursor cache and gives the
                 // clone its own reclaimer slot, so the clone and parent read

src/Lucene.Net/Support/Store/UnsafeChunkIndexInput.cs

@@ -146,7 +146,7 @@ protected UnsafeChunkIndexInput(DrainReclaimer reclaimer, string resourceDescrip
         /// disposed. Subclasses call this from <c>Clone()</c> (a disposed input
         /// must not hand out a working clone); the base calls it on the read paths.
         /// </summary>
-        protected void ThrowIfDisposed()
+        protected void EnsureOpen()
         {
             if (Volatile.Read(ref instanceClosed) != 0)
             {