Squelch an error that happens when the asset cache was mounted RO.

Nothing we can do about that, blame Docker.

OpenSim/Region/CoreModules/Asset/FlotsamAssetCache.cs

@@ -806,6 +806,9 @@ namespace OpenSim.Region.CoreModules.Asset
 
                     return;
                 }
+                catch (UnauthorizedAccessException e)
+                {
+                }
                 finally
                 {
                     if (stream != null)