patch 9.0.1571: RedrawingDisabled not used consistently

Problem:    RedrawingDisabled not used consistently.
Solution:   Avoid RedrawingDisabled going negative.  Set RedrawingDisabled in
            win_split_ins(). (closes #11961)
diff --git a/src/insexpand.c b/src/insexpand.c
index c20cb4f..3cfdfac 100644
--- a/src/insexpand.c
+++ b/src/insexpand.c
@@ -2969,12 +2969,13 @@
     void
 f_complete_check(typval_T *argvars UNUSED, typval_T *rettv)
 {
-    int		saved = RedrawingDisabled;
-
+    int save_RedrawingDisabled = RedrawingDisabled;
     RedrawingDisabled = 0;
+
     ins_compl_check_keys(0, TRUE);
     rettv->vval.v_number = ins_compl_interrupted();
-    RedrawingDisabled = saved;
+
+    RedrawingDisabled = save_RedrawingDisabled;
 }
 
 /*
@@ -5079,8 +5080,7 @@
 show_pum(int prev_w_wrow, int prev_w_leftcol)
 {
     // RedrawingDisabled may be set when invoked through complete().
-    int n = RedrawingDisabled;
-
+    int save_RedrawingDisabled = RedrawingDisabled;
     RedrawingDisabled = 0;
 
     // If the cursor moved or the display scrolled we need to remove the pum
@@ -5091,7 +5091,8 @@
 
     ins_compl_show_pum();
     setcursor();
-    RedrawingDisabled = n;
+
+    RedrawingDisabled = save_RedrawingDisabled;
 }
 
 /*