patch 8.2.1377: triggering the ATTENTION prompt causes typeahead mess up

Problem:    Triggering the ATTENTION prompt causes typeahead to be messed up.
Solution:   Increment tb_change_cnt. (closes #6541)

Author: brammool

src/getchar.c

@@ -447,6 +447,8 @@ flush_buffers(flush_buffers_T flush_typeahead)
     typebuf.tb_silent = 0;
     cmd_silent = FALSE;
     typebuf.tb_no_abbr_cnt = 0;
+    if (++typebuf.tb_change_cnt == 0)
+	typebuf.tb_change_cnt = 1;
 }
 
 /*

src/version.c

@@ -754,6 +754,8 @@ static char *(features[]) =
 
 static int included_patches[] =
 {   /* Add new patch number below this line */
+/**/
+    1377,
 /**/
     1376,
 /**/