Deal with XineramaQueryScreens failure.

The call to XineramaQueryScreens may return NULL in some cases. This patch
tries to deal with that somehow.

Signed-off-by: Tomas Janousek <tomi@nomi.cz>

src/Screen.cc

@@ -1955,6 +1955,7 @@ void BScreen::initXinerama() {
     Display *display = FbTk::App::instance()->display();
 
     if (!XineramaIsActive(display)) {
+notactive:
 #ifdef DEBUG
         cerr<<"BScreen::initXinerama(): dont have Xinerama"<<endl;
 #endif // DEBUG
@@ -1973,6 +1974,17 @@ void BScreen::initXinerama() {
     XineramaScreenInfo *screen_info;
     int number;
     screen_info = XineramaQueryScreens(display, &number);
+
+    /* The call may have actually failed. If this is the first time we init
+     * Xinerama, fall back to turning it off. If not, pretend nothing
+     * happened -- another event will tell us and it will work then. */
+    if (!screen_info) {
+        if (m_xinerama_headinfo)
+            return;
+        else
+            goto notactive;
+    }
+
     if (m_xinerama_headinfo)
         delete [] m_xinerama_headinfo;
     m_xinerama_headinfo = new XineramaHeadInfo[number];