patch 8.2.0839: dropping modifier when putting a character back in typeahead

Problem:    Dropping modifier when putting a character back in typeahead.
Solution:   Add modifier to ins_char_typebuf(). (closes #6158)
diff --git a/src/globals.h b/src/globals.h
index f0716c5..387c62e 100644
--- a/src/globals.h
+++ b/src/globals.h
@@ -120,7 +120,12 @@
  * When vgetc() is called, it sets mod_mask to the set of modifiers that are
  * held down based on the MOD_MASK_* symbols that are read first.
  */
-EXTERN int	mod_mask INIT(= 0x0);		// current key modifiers
+EXTERN int	mod_mask INIT(= 0);		// current key modifiers
+
+// The value of "mod_mask" and the unomdified character before calling
+// merge_modifyOtherKeys().
+EXTERN int	vgetc_mod_mask INIT(= 0);
+EXTERN int	vgetc_char INIT(= 0);
 
 /*
  * Cmdline_row is the row where the command line starts, just below the