make LLViewerTextureManager::staticCastToFetchedTexture to accept NULL pointer as input.
make LLViewerTextureManager::staticCastToFetchedTexture to accept NULL pointer as input.

gabeharms/firestorm,gabeharms/firestorm,gabeharms/firestorm,gabeharms/firestorm,gabeharms/firestorm,gabeharms/firestorm,gabeharms/firestorm,gabeharms/firestorm,gabeharms/firestorm