fixed bug in grass description loading

git-svn-id: http://sextante.googlecode.com/svn/trunk/soft/bindings/qgis-plugin@263 881b9c09-3ef8-f3c2-ec3d-21d735c97f4d

Author: volayaf

src/sextante/grass/GrassUtils.py

@@ -46,6 +46,8 @@ def grassPath():
             folder = plugin_installer.__file__
             idx = folder.find('qgis')
             folder = folder[:idx] + "grass"
+            if not os.path.isdir(folder):
+                return ""
             for subfolder in os.listdir(folder):
                 if subfolder.startswith("grass"):
                     folder = folder + os.sep + subfolder