TfsUserMappingTool Logic Error results in mapping file declaired missing even when not.

[MrHinsh]

Current implemention has a logic error where it will squash the found mapping file:

 private Dictionary<string, string> GetMappingFileData()
 {
     if (_UserMappings == null && System.IO.File.Exists(Options.UserMappingFile))
     {
         var fileData = System.IO.File.ReadAllText(Options.UserMappingFile);
         try
         {
             var fileMaps = Newtonsoft.Json.JsonConvert.DeserializeObject<List<IdentityMapData>>(fileData);
             _UserMappings = fileMaps.ToDictionary(x => x.Source.FriendlyName, x => x.target?.FriendlyName);
         }
         catch (Exception)
         {
             _UserMappings = new Dictionary<string, string>();
             Log.LogError($"TfsUserMappingTool::GetMappingFileData [UserMappingFile|{Options.UserMappingFile}] <-- invalid - No mapping are applied!");
         }

     }
     else
     {
         Log.LogError($"TfsUserMappingTool::GetMappingFileData::No User Mapping file Provided! Provide file or disable TfsUserMappingTool");
         _UserMappings = new Dictionary<string, string>();
     }

     return _UserMappings;

 }

proposed replacement is :

       private Dictionary<string, string> GetMappingFileData()
       {
           if (!System.IO.File.Exists(Options.UserMappingFile))
           {
               Log.LogError($"TfsUserMappingTool::GetMappingFileData::No User Mapping file Provided! Provide file or disable TfsUserMappingTool");
               _UserMappings = new Dictionary<string, string>();
           }
           if (_UserMappings == null )
           {
               var fileData = System.IO.File.ReadAllText(Options.UserMappingFile);
               try
               {
                   var fileMaps = Newtonsoft.Json.JsonConvert.DeserializeObject<List<IdentityMapData>>(fileData);
                   _UserMappings = fileMaps.ToDictionary(x => x.Source.FriendlyName, x => x.target?.FriendlyName);
               }
               catch (Exception)
               {
                   _UserMappings = new Dictionary<string, string>();
                   Log.LogError($"TfsUserMappingTool::GetMappingFileData [UserMappingFile|{Options.UserMappingFile}] <-- invalid - No mapping are applied!");
               }

           }
           return _UserMappings;
       }