files: give feedback when restricted mode prevents overwriting a file

Achieve this by reusing the code that gives feedback when trying to
save a buffer while using --tempfile and the file has no name yet.

This fixes https://savannah.gnu.org/bugs/?48622.

src/files.c

@@ -2370,8 +2370,11 @@ int do_writeout(bool exiting)
 		     * of the current file if it has one, because that
 		     * would allow reading from or writing to files not
 		     * specified on the command line. */
-		    if (ISSET(RESTRICTED))
+		    if (ISSET(RESTRICTED)) {
+			warn_and_shortly_pause(_("File exists -- "
+					"cannot overwrite"));
 			continue;
+		    }
 
 		    if (!maychange) {
 #ifndef NANO_TINY

src/nano.c

@@ -1058,21 +1058,6 @@ void version(void)
     printf("\n");
 }
 
-/* Indicate that the current file has no name, in a way that gets the
- * user's attention.  This is used when trying to save a file with no
- * name with the TEMP_FILE flag set, just before the filename prompt. */
-void no_current_file_name_warning(void)
-{
-    /* Warn that the current file has no name. */
-    statusbar(_("No file name"));
-    beep();
-
-    /* Ensure that we see the warning. */
-    napms(1800);
-
-    curs_set(1);
-}
-
 /* If the current file buffer has been modified, and the TEMP_FILE flag
  * isn't set, ask whether or not to save the file buffer.  If the
  * TEMP_FILE flag is set and the current file has a name, save it
@@ -1096,7 +1081,7 @@ void do_exit(void)
 	/* If the TEMP_FILE flag is set, and the current file doesn't
 	 * have a name, warn the user before prompting for a name. */
 	if (ISSET(TEMP_FILE))
-	    no_current_file_name_warning();
+	    warn_and_shortly_pause(_("No file name"));
 
 	i = do_yesno_prompt(FALSE, _("Save modified buffer?  "
 			"(Answering \"No\" will DISCARD changes.) "));

src/proto.h

@@ -456,7 +456,6 @@ void print_opt_full(const char *shortflag
 	, const char *desc);
 void usage(void);
 void version(void);
-void no_current_file_name_warning(void);
 void do_exit(void);
 void close_and_go(void);
 void signal_init(void);
@@ -739,6 +738,7 @@ char *display_string(const char *buf, size_t start_col, size_t span,
 void titlebar(const char *path);
 extern void set_modified(void);
 void statusbar(const char *msg);
+void warn_and_shortly_pause(const char *msg);
 void statusline(message_type importance, const char *msg, ...);
 void bottombars(int menu);
 void onekey(const char *keystroke, const char *desc, int length);

src/winio.c

@@ -2070,6 +2070,17 @@ void statusbar(const char *msg)
     statusline(HUSH, msg);
 }
 
+/* Warn the user on the statusbar and pause for a moment, so that the
+ * message can be noticed and read. */
+void warn_and_shortly_pause(const char *msg)
+{
+    statusbar(msg);
+    beep();
+    napms(1800);
+
+    curs_set(1);
+}
+
 /* Display a message on the statusbar, and set suppress_cursorpos to
  * TRUE, so that the message won't be immediately overwritten if
  * constant cursor position display is on. */