patch 8.2.4173: cannot use an import in 'foldexpr'

Problem:    Cannot use an import in 'foldexpr'.
Solution:   Set the script context to where 'foldexpr' was set. (closes #9584)
            Fix that the script context was not set for all buffers.
diff --git a/src/structs.h b/src/structs.h
index f733268..e2f1de9 100644
--- a/src/structs.h
+++ b/src/structs.h
@@ -3695,6 +3695,8 @@
      */
     winopt_T	w_onebuf_opt;
     winopt_T	w_allbuf_opt;
+    // transform a pointer to a "onebuf" option into a "allbuf" option
+#define GLOBAL_WO(p)	((char *)p + sizeof(winopt_T))
 
     // A few options have local flags for P_INSECURE.
 #ifdef FEAT_STL_OPT
@@ -3718,9 +3720,6 @@
     int		w_briopt_list;      // additional indent for lists
 #endif
 
-    // transform a pointer to a "onebuf" option into a "allbuf" option
-#define GLOBAL_WO(p)	((char *)p + sizeof(winopt_T))
-
     long	w_scbind_pos;
 
 #ifdef FEAT_EVAL