patch 8.2.1729: endless loop when ":normal" feeds popup window filter

Problem:    Endless loop when ":normal" feeds popup window filter.
Solution:   Add the ex_normal_busy_done flag.
diff --git a/src/globals.h b/src/globals.h
index 94164bb..eb33507 100644
--- a/src/globals.h
+++ b/src/globals.h
@@ -1152,6 +1152,11 @@
 		    ;
 EXTERN int	ex_normal_busy INIT(= 0); // recursiveness of ex_normal()
 EXTERN int	ex_normal_lock INIT(= 0); // forbid use of ex_normal()
+#ifdef FEAT_PROP_POPUP
+// Set to TRUE when ex_normal_busy is set and out of typeahead.
+EXTERN int	ex_normal_busy_done INIT(= FALSE);
+#endif
+
 #ifdef FEAT_EVAL
 EXTERN int	ignore_script INIT(= FALSE);  // ignore script input
 #endif