Now using view->fopen() to stream file contents to clamav

- Now always streaming the file's contents to clamav
- Fixes #1384 where a user uploads a file to a read-write shared dir
- Fixes case with encryption enabled

Backport of 42431e57e0f2ee221b51729e4ea1e62e2cf505e5 (without socket
part)
Use storage to unlink the virus file
Merge branch 'stable5-antivirus-viewfopenstream' into stable5