Flip operands

This avoids accessing the b:python_modified value, which under some
circumstances cannot be set, which results in the following error:

    Error detected while processing function pymode#buffer_post_write:
    line    2:
    E121: Undefined variable: b:pymode_modified
    E15: Invalid expression: b:pymode_modified && g:pymode_rope_regenerate_on_write

Note that this does not address the core issue with why pymode_modified
if unset in the first place, but this avoids that being a problem if
g:python_rope_regenerate_on_write is not wanted anyway.

Author: nvie

autoload/pymode.vim

@@ -113,7 +113,7 @@ endfunction "}}}
 
 fun! pymode#buffer_post_write() "{{{
     if g:pymode_rope
-        if b:pymode_modified && g:pymode_rope_regenerate_on_write
+        if g:pymode_rope_regenerate_on_write && b:pymode_modified
             call pymode#debug('regenerate')
             call pymode#rope#regenerate()
         endif