Call XdbeQueryExtension before of calling any Xdbe function

XdbeQueryExtension() tells to the caller if the Xdbe extension is present in
the X server, so it should be called for sanity. But like is said in
XdbeQueryExtension(3):

	No other Xdbe functions may be called before this function.  If a
	client violates this rule, the effects of all subsequent Xdbe calls
	that it makes are undefined.

it is mandatory call this function.
---
 st.c |    5 +++--
 1 file changed, 3 insertions(+), 2 deletions(-)

1 files changed, 3 insertions, 2 deletions

diff --git a/st.c b/st.c
index 2e1ac67..b013bca 100644
--- a/st.c
+++ b/st.c
@@ -1970,7 +1970,7 @@ xinit(void) {
         XSetWindowAttributes attrs;
         Cursor cursor;
         Window parent;
-        int sw, sh;
+        int sw, sh, major, minor;
 
         if(!(xw.dpy = XOpenDisplay(NULL)))
                 die("Can't open display\n");
@@ -2021,9 +2021,10 @@ xinit(void) {
                         CWBackPixel | CWBorderPixel | CWBitGravity | CWEventMask
                         | CWColormap,
                         &attrs);
+        if(!XdbeQueryExtension(xw.dpy, &major, &minor))
+                die("Xdbe extension is not present\n");
         xw.buf = XdbeAllocateBackBufferName(xw.dpy, xw.win, XdbeCopied);
 
-
         /* input methods */
         xw.xim = XOpenIM(xw.dpy, NULL, NULL, NULL);
         xw.xic = XCreateIC(xw.xim, XNInputStyle, XIMPreeditNothing