patch 9.0.0940: crash when typing a letter in a terminal window

Problem:    Crash when typing a letter in a terminal window. (Shane-XB-Qian)
Solution:   Use the "vterm" variable instead of getting the terminal pointer
            from the current buffer.  (closes #11608)
diff --git a/src/terminal.c b/src/terminal.c
index d0cdd45..bc36317 100644
--- a/src/terminal.c
+++ b/src/terminal.c
@@ -1590,7 +1590,7 @@
     // Ctrl-Shift-i may have the key "I" instead of "i", but for the kitty
     // keyboard protocol should use "i".  Applies to all ascii letters.
     if (ASCII_ISUPPER(c)
-	    && vterm_is_kitty_keyboard(curbuf->b_term->tl_vterm)
+	    && vterm_is_kitty_keyboard(vterm)
 	    && mod == (VTERM_MOD_CTRL | VTERM_MOD_SHIFT))
 	c = TOLOWER_ASC(c);