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(-)