g.extension: inform user when no extension is installed (-a)

git-svn-id: https://svn.osgeo.org/grass/grass/trunk@49742 15284696-431f-4ddb-bdfa-cd5b030d7da7

scripts/g.extension/g.extension.py

@@ -706,10 +706,12 @@ def main():
         list_available_extensions()
         return 0
     elif flags['a']:
-        grass.message(_("List of installed extensions:"))
         elist = get_installed_extensions()
         if elist:
+            grass.message(_("List of installed extensions:"))
             print os.linesep.join(elist)
+        else:
+            grass.info(_("No extension installed"))
         return 0
     else:
         if not options['extension']: