Improve performance of QLibrary::load()

Improve performance of QLibrary::load()

There is no need to create a QFileInfo object to split the path and
filename.

Change-Id: I54ebb4b62ebdd93a257bce0b337ac0012f0d5a56
Reviewed-by: James Turner <james.turner@kdab.com>
Reviewed-by: Rafael Roquetto <rafael.roquetto@kdab.com>
Reviewed-by: Marc Mutz <marc.mutz@kdab.com>
Reviewed-by: João Abecasis <joao.abecasis@nokia.com>
Reviewed-by: Lars Knoll <lars.knoll@nokia.com>
Reviewed-by: Andreas Holzammer <andreas.holzammer@kdab.com>
Reviewed-by: Thiago Macieira <thiago.macieira@intel.com>
Reviewed-by: Giuseppe D'Angelo <giuseppe.dangelo@kdab.com>