buflist: return 0 if buffers are equal in sort function

This is better for symmetry of comparison callback (comparing buffer1 and
buffer2 will give same as comparing buffer2 and bufer1).

Thanks to Simmo Saan for reporting the problem.

src/plugins/buflist/buflist.c

@@ -320,7 +320,7 @@ buflist_compare_buffers (void *data, struct t_arraylist *arraylist,
             return rc;
     }
 
-    return 1;
+    return 0;
 }
 
 /*