patch 9.0.1126: bracketed paste can be enabled when it is not recognized

Problem:    Bracketed paste can be enabled when pasted text is not recognized.
Solution:   Output t_BE only when t_PS and t_PE are set.
diff --git a/src/proto/term.pro b/src/proto/term.pro
index 93edba1..8c8b813 100644
--- a/src/proto/term.pro
+++ b/src/proto/term.pro
@@ -49,6 +49,7 @@
 void set_shellsize(int width, int height, int mustset);
 void out_str_t_TE(void);
 void out_str_t_TI(void);
+void out_str_t_BE(void);
 void may_send_t_RK(void);
 void settmode(tmode_T tmode);
 void starttermcap(void);