C++ API: Add support to open devices with missing product / serial strings

C++ API: Add support to open devices with missing product / serial strings

The C++ API and C API differ in how they open a device. The C API only
considers the user supplied strings iVendor, iProduct and iSerial to open a device.

The C++ API behaves differently. After opening the device with specific supplied strings,
it tries to read all strings via get_strings_and_reopen().
This fails if one string like iSerial is not defined
in the descriptor. As such the whole open() operation fails
and the C++ API would only open devices with complete descriptors.

This commit fixes this behaviour, by extending the get_strings_and_reopen()
and get_strings() argument lists, to configure the strings to read.