4591: Do not allow less than a single column in the Gramplet view

svn: r16547

src/gui/widgets/grampletpane.py

@@ -1227,6 +1227,8 @@ class GrampletPane(gtk.ScrolledWindow):
         return True
 
     def set_columns(self, num):
+        if num < 1:
+            num = 1
         # clear the gramplets:
         self.clear_gramplets()
         # clear the columns: