Omit empty internal SD Card readers on Windows
Omit empty internal SD Card readers on Windows

Windows lists internal SD Card readers by default, even when they have
no SD Card inserted on them. As a solution, we can check if the size
returned for such internal reader is `null`, and if so, omit it from the
final drive list.

Signed-off-by: Juan Cruz Viotti <4148f5869aa1bcd7efd85b513a5874967e585032@openmailbox.org>

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