delete-or-exit: Only exit if the commandline is empty

This exitted if the cursor was at the end of the line as well (i.e. if
delete-char failed). That's a bit too eager.

Also documentation, which should have already been included.

sphinx_doc_src/cmds/bind.rst

@@ -102,6 +102,8 @@ The following special input functions are available:
 
 - ``delete-char``, delete one character to the right of the cursor
 
+- ``delete-or-exit``, deletes one character to the right of the cursor or exits the shell if the commandline is empty.
+
 - ``downcase-word``, make the current word lowercase
 
 - ``end-of-buffer``, moves to the end of the buffer, i.e. the end of the first line

src/reader.cpp

@@ -2682,7 +2682,7 @@ void reader_data_t::handle_readline_command(readline_cmd_t c, readline_loop_stat
             if (el->position < el->size()) {
                 update_buff_pos(el, el->position + 1);
                 remove_backward();
-            } else if (c == rl::delete_or_exit) {
+            } else if (c == rl::delete_or_exit && el->empty()) {
                 reader_set_end_loop(true);
             }
             break;