[jhbuild/BUG_sys_regression] defaults.jhbuildrc: fix regression

[Nelson Ben <nbenitez src gnome org>]

commit 67d4c1c7a3bf4185a6899f772e17cd09db4b4518
Author: Nelson Benítez León <nbenitezl gmail com>
Date:   Tue Jun 30 20:59:09 2020 -0400

    defaults.jhbuildrc: fix regression
    
    on previous commit, see #67 for details.

 jhbuild/defaults.jhbuildrc | 2 +-
 1 file changed, 1 insertion(+), 1 deletion(-)
---
diff --git a/jhbuild/defaults.jhbuildrc b/jhbuild/defaults.jhbuildrc
index dc99e7e9..097dd1ba 100644
--- a/jhbuild/defaults.jhbuildrc
+++ b/jhbuild/defaults.jhbuildrc
@@ -145,7 +145,7 @@ export_dir = None
 
 # attempt to detect the system library path
 extra_prefixes = []
-if hasattr(sys.implementation, '_multiarch') and \
+if hasattr(sys, 'implementation') and hasattr(sys.implementation, '_multiarch') and \
    os.path.exists('/usr/lib/' + sys.implementation._multiarch):
     # Debian-style multiarch
     system_libdirs = ['/usr/lib/' + sys.implementation._multiarch, '/usr/lib']