no crash when display was wrong

TODO

 immediate:
 ----------
 
-x11vnc: clipboard, cursor, updates interruptible by input
+x11vnc: clipboard, cursor, updates interruptible by input,
+	sometimes XTest fails (but doesn't with x0rfbserver)
 extra_bytes in rfbDrawCharWithClip.
 tested mouse buttons make copy rect, but text is not marked as mod.
 cursor drawing: set optional grain to mark bigger rectangles as drawn (else

x11vnc.c

@@ -243,6 +243,11 @@ int main(int argc,char** argv)
 
   if(dpy==0)
     dpy = XOpenDisplay("");
+  if(dpy==0) {
+    fprintf(stderr,"Couldn't open display!\n");
+    exit(2);
+  }
+     
   xscreen = DefaultScreen(dpy);
 
   init_keycodes();