[patch] SEGV occurs in balloon_show() under certain circumstances.

[h_east]

Hi Bram,

How to reproduce (on Linux):
- Go to Vim source directory
  $ cd /path/to/your/vim
- Configure with enabling gui gnome2
  $ ./configure --with-features=huge --enable-gui=gnome2 
--enable-fail-if-missing
- Make
  $ make
- Run vanilla CLI Vim
  $ src/vim -Nu NONE
- Execute the following command.
  :call balloon_show("Hi")

Expected behavior:
- Nothing happens. (Or an error message is output?)

Actual behavior:
- SEGV

Attached patch fixes this.

--
Best regards,
Hirohito Higashi (a.k.a. h_east)

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diff --git a/src/gui_beval.c b/src/gui_beval.c
index dd61945..a63ede4 100644
--- a/src/gui_beval.c
+++ b/src/gui_beval.c
@@ -437,6 +437,9 @@ get_beval_info(
     void
 gui_mch_post_balloon(BalloonEval *beval, char_u *mesg)
 {
+    if (beval == NULL)
+	return;
+
     beval->msg = mesg;
     if (mesg != NULL)
 	drawBalloon(beval);
diff --git a/src/gui_w32.c b/src/gui_w32.c
index cd9f31e..13ea26f 100644
--- a/src/gui_w32.c
+++ b/src/gui_w32.c
@@ -8582,7 +8582,7 @@ gui_mch_post_balloon(BalloonEval *beval, char_u *mesg)
 {
     POINT   pt;
     // TRACE0("gui_mch_post_balloon {{{");
-    if (beval->showState == ShS_SHOWING)
+    if (beval == NULL || beval->showState == ShS_SHOWING)
 	return;
     GetCursorPos(&pt);
     ScreenToClient(s_textArea, &pt);