package/gobject-introspection/g-ir-scanner-qemuwrapper.in: Fix latent bug if GIR_EXTR...

package/gobject-introspection/g-ir-scanner-qemuwrapper.in: Fix latent bug if GIR_EXTRA_LIBS_PATH is empty

If GIR_EXTRA_LIBS_PATH is empty, the LD_LIBRARY_PATH variable is
":.libs:$(dirname $0)/../lib:$(dirname $0)/../../lib".

As discussed with Yann Morin, add a new variable, "GOI_LIBRARY_PATH" and
prepend ${GIR_EXTRA_LIBS_PATH:+${GIR_EXTRA_LIBS_PATH}:} to the path to fix the
above bug.

Signed-off-by: Adam Duskett <aduskett@gmail.com>
Signed-off-by: Arnout Vandecappelle (Essensium/Mind) <arnout@mind.be>