patch 8.2.0013: not using a typedef for condstack

Problem:    Not using a typedef for condstack.
Solution:   Add a typedef.
diff --git a/src/userfunc.c b/src/userfunc.c
index 020098d..948c5f1 100644
--- a/src/userfunc.c
+++ b/src/userfunc.c
@@ -3234,7 +3234,7 @@
     void	*rettv)
 {
     int		idx;
-    struct condstack *cstack = eap->cstack;
+    cstack_T	*cstack = eap->cstack;
 
     if (reanimate)
 	// Undo the return.