Added null checks in AssetManager to prevent exceptions when alternative upload methods are used
Added null checks in AssetManager to prevent exceptions when alternative upload methods are used

git-svn-id: c32cf1ecefca26b8770d7b0740bc0c5c174087e4@1185 c754d5e9-d413-0410-bcdf-9574c9dba6b7

jhs/libopenmetaverse,jhs/libopenmetaverse,jhs/libopenmetaverse,jhs/libopenmetaverse