Fix EventLog test CanReadAndWriteMessages

[carlossanlop]

Fixes #88224

I ran this in an elevated console and it failed with the reported error:

===========================================================================================================
    Discovering: System.Diagnostics.EventLog.Tests (method display = ClassAndMethod, method display options = None)
    Discovered:  System.Diagnostics.EventLog.Tests (found 123 of 125 test cases)
    Starting:    System.Diagnostics.EventLog.Tests (parallel test collections = on, max threads = 16)
      System.Diagnostics.Tests.EventLogMessagesTests.CanReadAndWriteMessages [FAIL]
        Assert.Equal() Failure
                                         � (pos 42)
        Expected: ···1b-86c3-93c25c528d55
        Actual:   ···1b-86c3-93c25c528d55\0
                                         � (pos 42)
        Stack Trace:
          C:\Users\calope\source\repos\runtime\src\libraries\System.Diagnostics.EventLog\tests\EventLogMessagesTests.cs(80,0): at System.Diagnostics.
  Tests.EventLogMessagesTests.CanReadAndWriteMessages()
             at System.RuntimeMethodHandle.InvokeMethod(Object target, Void** arguments, Signature sig, Boolean isConstructor)
          C:\Users\calope\source\repos\runtime\src\coreclr\System.Private.CoreLib\src\System\Reflection\MethodBaseInvoker.CoreCLR.cs(36,0): at System
  .Reflection.MethodBaseInvoker.InterpretedInvoke_Method(Object obj, IntPtr* args)
          C:\Users\calope\source\repos\runtime\src\libraries\System.Private.CoreLib\src\System\Reflection\MethodBaseInvoker.cs(57,0): at System.Refle
  ction.MethodBaseInvoker.InvokeWithNoArgs(Object obj, BindingFlags invokeAttr)

It seems the problem is that the buffer may end up with multiple null terminators, so I adjusted the code to make sure we remove them all.

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Issue Details

---

We have many EventLog tests that are executed if the process is elevated but we never run them with RemoteExecutor. I am investigating if this could help them pass.

I ran this in an elevated console and it failed with an error stating that it still had a null terminator, even though we removed it:

===========================================================================================================
    Discovering: System.Diagnostics.EventLog.Tests (method display = ClassAndMethod, method display options = None)
    Discovered:  System.Diagnostics.EventLog.Tests (found 123 of 125 test cases)
    Starting:    System.Diagnostics.EventLog.Tests (parallel test collections = on, max threads = 16)
      System.Diagnostics.Tests.EventLogMessagesTests.CanReadAndWriteMessages [FAIL]
        Assert.Equal() Failure
                                         � (pos 42)
        Expected: ···1b-86c3-93c25c528d55
        Actual:   ···1b-86c3-93c25c528d55\0
                                         � (pos 42)
        Stack Trace:
          C:\Users\calope\source\repos\runtime\src\libraries\System.Diagnostics.EventLog\tests\EventLogMessagesTests.cs(80,0): at System.Diagnostics.
  Tests.EventLogMessagesTests.CanReadAndWriteMessages()
             at System.RuntimeMethodHandle.InvokeMethod(Object target, Void** arguments, Signature sig, Boolean isConstructor)
          C:\Users\calope\source\repos\runtime\src\coreclr\System.Private.CoreLib\src\System\Reflection\MethodBaseInvoker.CoreCLR.cs(36,0): at System
  .Reflection.MethodBaseInvoker.InterpretedInvoke_Method(Object obj, IntPtr* args)
          C:\Users\calope\source\repos\runtime\src\libraries\System.Private.CoreLib\src\System\Reflection\MethodBaseInvoker.cs(57,0): at System.Refle
  ction.MethodBaseInvoker.InvokeWithNoArgs(Object obj, BindingFlags invokeAttr)

It seems the problem is that the buffer may end up with multiple null terminators, so I removed them.

The test now passes locally in an elevated console in Win11 arm64. Now I need to see the CI results.

Author:	carlossanlop
Assignees:	carlossanlop
Labels:	NO-MERGE, NO-REVIEW, area-System.Diagnostics.EventLog
Milestone:	-