mined: fix buffer overflow in input()

input() is used to accept filenames when saving, regular
expressions when searching, and other input. It writes
the characters into buffers such as file and exp_buf and
others which are of length LINE_LEN.

To prevent writing beyond the end of the intended buffer,
truncate the input at LINE_LEN - 1 and ensure that the
string is NULL terminated.

minix/usr.bin/mined/mined1.c

@@ -1694,6 +1694,9 @@ int input(char *inbuf, FLAG clearfl)
   			}
   			else
   				ring_bell();
+
+			if (ptr - inbuf >= LINE_LEN - 1)
+				return FINE;
   	}
   }
   quit = FALSE;