Previously we were only attempting to obtain a handle to an already
loaded sibling library residing in the same directory. If it wasn't
already pre-loaded, we only loaded the library by name without any
directory prefix. This could lead to not finding the correct library.

Also, it's fine if the directory prefix is empty, so there's no need for
duplicate loops.

Bug b/110407478

Change-Id: Ia55b426e58b9f4039064bba9253dae80e4fdf5cf
Reviewed-on: https://swiftshader-review.googlesource.com/19549Tested-by: Nicolas Capens <nicolascapens@google.com>
Reviewed-by: Alexis Hétu <sugoi@google.com>