patch 8.0.1217: can't use remote eval to inspect vars in debug mode

Problem:    Can't use remote eval to inspect vars in debug mode.
Solution:   Don't discard the call stack in debug mode. (closes #2237, #2247)
diff --git a/src/ex_cmds2.c b/src/ex_cmds2.c
index e9a9a6d..2eef050 100644
--- a/src/ex_cmds2.c
+++ b/src/ex_cmds2.c
@@ -131,6 +131,7 @@
     redir_off = TRUE;		/* don't redirect debug commands */
 
     State = NORMAL;
+    debug_mode = TRUE;
 
     if (!debug_did_msg)
 	MSG(_("Entering Debug mode.  Type \"cont\" to continue."));
@@ -319,6 +320,7 @@
     msg_scroll = save_msg_scroll;
     lines_left = Rows - 1;
     State = save_State;
+    debug_mode = FALSE;
     did_emsg = save_did_emsg;
     cmd_silent = save_cmd_silent;
     msg_silent = save_msg_silent;