Return empty list if a map doesn't have any entries

If a map doesn't have entries haproxy returns an empty string.
Returning one element list with an empty string isn't the right approach.
Close #6

haproxyadmin/haproxy.py

@@ -953,7 +953,10 @@ def show_map(self, mapid=None):
         if not check_output(map_info_proc1):
             raise CommandFailed(map_info_proc1[0])
 
-        return map_info_proc1
+        if len(map_info_proc1) == 1 and not map_info_proc1[0]:
+            return []
+        else:
+            return map_info_proc1
 
     @property
     def uptime(self):