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/main.c b/src/main.c
index 0dad4d6..0283231 100644
--- a/src/main.c
+++ b/src/main.c
@@ -4180,11 +4180,12 @@
     char_u	*res;
     int		save_dbl = debug_break_level;
     int		save_ro = redir_off;
-    void	*fc;
+    void	*fc = NULL;
 
     /* Evaluate the expression at the toplevel, don't use variables local to
-     * the calling function. */
-    fc = clear_current_funccal();
+     * the calling function. Except when in debug mode. */
+    if (!debug_mode)
+	fc = clear_current_funccal();
 
      /* Disable debugging, otherwise Vim hangs, waiting for "cont" to be
       * typed. */
@@ -4201,7 +4202,8 @@
     --emsg_silent;
     if (emsg_silent < 0)
 	emsg_silent = 0;
-    restore_current_funccal(fc);
+    if (fc != NULL)
+	restore_current_funccal(fc);
 
     /* A client can tell us to redraw, but not to display the cursor, so do
      * that here. */