patch 9.0.0904: various comment and indent flaws

Problem:    Various comment and indent flaws.
Solution:   Improve comments and indenting.

src/evalwindow.c

@@ -89,6 +89,7 @@ win_id2wp(int id)
 
 /*
  * Return the window and tab pointer of window "id".
+ * Returns NULL when not found.
  */
     win_T *
 win_id2wp_tp(int id, tabpage_T **tpp)