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(-)

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