bin/install_megadrivers.py: Fix regression for set DESTDIR

The previous patch tried to address a bug when DESTDIR is '', however,
it introduces a bug when DESTDIR is not '', and fakeroot is used. This
patch does fix that, and has been tested with the arch pkg-build to
ensure it isn't regressed.

Fixes: 093a1ade4e24b7dd701a093d30a71efd669fe9c8
       ("bin/install_megadrivers.py: Correctly handle DESTDIR=''")
Bugzilla: https://bugs.freedesktop.org/show_bug.cgi?id=110221
Reviewed-by: Eric Engestrom <eric@engestrom.ch>

bin/install_megadrivers.py

@@ -35,7 +35,11 @@ def main():
     args = parser.parse_args()
 
     if os.path.isabs(args.libdir):
-        to = os.path.join(os.environ.get('DESTDIR', ''), args.libdir)
+        destdir = os.environ.get('DESTDIR')
+        if destdir:
+            to = os.path.join(destdir, args.libdir[1:])
+        else:
+            to = args.libdir
     else:
         to = os.path.join(os.environ['MESON_INSTALL_DESTDIR_PREFIX'], args.libdir)