Run cleanup message in RevertItem

[PhilJollans]

I have received this report by Email on 23-Sep-2020

SharpSvn.SvnWorkingCopyException: Previous operation has not finished; run 'cleanup' if it was interrupted
   at SharpSvn.SvnClientArgs.HandleResult(SvnClientContext client, SvnException error, Object targets)
   at SharpSvn.SvnClientArgs.HandleResult(SvnClientContext client, svn_error_t* error, Object targets)
   at SharpSvn.SvnClient.Revert(ICollection`1 paths, SvnRevertArgs args)
   at SharpSvn.SvnClient.Revert(String path, SvnRevertArgs args)
   at Ankh.Commands.RevertItemCommand.<>c__DisplayClass1_0.<OnExecute>b__2(Object sender, ProgressWorkerArgs a)
   at Ankh.ProgressRunnerService.ProgressRunner.Run(Object arg)

svn-version=1.9.5
os-version=10.0.16299.0
ankh-version=1.0.0.10
sharpsvn-version=1.9005.3940.224
command=RevertItem
vs-version=16.0.30501.64

I don't think that we can fix this error, but it would be nice to show the message

Previous operation has not finished; run 'cleanup' if it was interrupted

as a message box, rather than an error report.