add platform test to directory picker

MediaBrowser.Api/EnvironmentService.cs

@@ -134,6 +134,8 @@ namespace MediaBrowser.Api
         {
             var result = new DefaultDirectoryBrowserInfo();
 
+            if (Environment.OSVersion.Platform == PlatformID.Unix)
+            {
                 try
                 {
                     var qnap = "/share/CACHEDEV1_DATA";
@@ -146,6 +148,7 @@ namespace MediaBrowser.Api
                 {
 
                 }
+            }
 
             return ToOptimizedResult(result);
         }