Fix bug where having no maximum memory cache timeout would cause the flotsam asset cache to try using Double.MaxValue, which would cause the underlying OpenMetaverse.ExpiringCache to choke.

There is probably an underlying bug to fix in ExpiringCache.

OpenSim/Region/CoreModules/Asset/FlotsamAssetCache.cs

@@ -252,7 +252,7 @@ namespace Flotsam.RegionModules.AssetCache
                 }
                 else
                 {
-                    m_MemoryCache.AddOrUpdate(key, asset, Double.MaxValue);
+                    m_MemoryCache.AddOrUpdate(key, asset, m_DefaultMemoryExpiration);
                 }
             }
         }