NRTCachingDirectory doesn't allow double dispose calls

[NightOwl888]

Per the dispose pattern docs:

✓ DO allow the Dispose(bool) method to be called more than once. The method might choose to do nothing after the first call.

X AVOID throwing an exception from within Dispose(bool) except under critical situations where the containing process has been corrupted (leaks, inconsistent shared state, etc.).

NRTCachingDirectory violates both of these rules by throwing an ObjectDisposedException the second time Dispose() is called. We need to be careful about how to fix this and ensure the usage pattern will work after the fix has been applied.

System.ObjectDisposedException : this Directory is disposed.
Object name: 'Lucene.Net.Store.RAMDirectory'.

To reproduce this test result:

Option 1:

Apply the following assembly-level attributes:

[assembly: Lucene.Net.Util.RandomSeed("0xc6267c4598373666")]
[assembly: NUnit.Framework.SetCulture("gd")]

Option 2:

Use the following .runsettings file:

<RunSettings>
<TestRunParameters>
<Parameter name="tests:seed" value="0xc6267c4598373666" />
<Parameter name="tests:culture" value="gd" />
</TestRunParameters>
</RunSettings>

See the .runsettings documentation at: https://docs.microsoft.com/en-us/visualstudio/test/configure-unit-tests-by-using-a-dot-runsettings-file.
at Lucene.Net.Store.BaseDirectory.EnsureOpen() in /_/src/Lucene.Net/Store/BaseDirectory.cs:line 77
at Lucene.Net.Store.RAMDirectory.ListAll() in /_/src/Lucene.Net/Store/RAMDirectory.cs:line 123
at Lucene.Net.Store.NRTCachingDirectory.Dispose(Boolean disposing) in /_/src/Lucene.Net/Store/NRTCachingDirectory.cs:line 362
at Lucene.Net.Store.MockDirectoryWrapper.Dispose(Boolean disposing) in /_/src/Lucene.Net.TestFramework/Store/MockDirectoryWrapper.cs:line 1108
at Lucene.Net.Store.Directory.Dispose() in /_/src/Lucene.Net/Store/Directory.cs:line 134
at Lucene.Net.Index.TestIndexWriterOnJRECrash.CheckIndexes(FileSystemInfo file) in /_/src/Lucene.Net.Tests/Index/TestIndexWriterOnJRECrash.cs:line 324
at Lucene.Net.Index.TestIndexWriterOnJRECrash.TestNRTThreads_Mem() in /_/src/Lucene.Net.Tests/Index/TestIndexWriterOnJRECrash.cs:line 87
at System.RuntimeMethodHandle.InvokeMethod(Object target, Void** arguments, Signature sig, Boolean isConstructor)
at System.Reflection.MethodInvoker.Invoke(Object obj, IntPtr* args, BindingFlags invokeAttr)