present: fallback get_crtc to return crtc belonging to screen with present extension

Since crtc can belong to secondary output that may not have present
extension enabled we should fallback to first enabled crtc or fake crtc.

Fix for issue xorg/xserver#1195

present/present.c

@@ -44,11 +44,19 @@ present_get_crtc(WindowPtr window)
 {
     ScreenPtr                   screen = window->drawable.pScreen;
     present_screen_priv_ptr     screen_priv = present_screen_priv(screen);
+    RRCrtcPtr                   crtc = NULL;
 
     if (!screen_priv)
         return NULL;
 
-    return screen_priv->get_crtc(screen_priv, window);
+    crtc = screen_priv->get_crtc(screen_priv, window);
+    if (crtc && !present_screen_priv(crtc->pScreen)) {
+        crtc = RRFirstEnabledCrtc(screen);
+    }
+    if (crtc && !present_screen_priv(crtc->pScreen)) {
+        crtc = NULL;
+    }
+    return crtc;
 }
 
 /*

randr/randr.c

@@ -697,6 +697,33 @@ RRFirstOutput(ScreenPtr pScreen)
     return NULL;
 }
 
+RRCrtcPtr
+RRFirstEnabledCrtc(ScreenPtr pScreen)
+{
+    rrScrPriv(pScreen);
+    RROutputPtr output;
+    int i, j;
+
+    if (!pScrPriv)
+        return NULL;
+
+    if (pScrPriv->primaryOutput && pScrPriv->primaryOutput->crtc &&
+        pScrPriv->primaryOutput->pScreen == pScreen)
+        return pScrPriv->primaryOutput->crtc;
+
+    for (i = 0; i < pScrPriv->numCrtcs; i++) {
+        RRCrtcPtr crtc = pScrPriv->crtcs[i];
+
+        for (j = 0; j < pScrPriv->numOutputs; j++) {
+            output = pScrPriv->outputs[j];
+            if (output->crtc == crtc && crtc->mode)
+                return crtc;
+        }
+    }
+    return NULL;
+}
+
+
 CARD16
 RRVerticalRefresh(xRRModeInfo * mode)
 {

randr/randrstr.h

@@ -593,6 +593,8 @@ extern _X_EXPORT Bool RRScreenInit(ScreenPtr pScreen);
 
 extern _X_EXPORT RROutputPtr RRFirstOutput(ScreenPtr pScreen);
 
+extern _X_EXPORT RRCrtcPtr RRFirstEnabledCrtc(ScreenPtr pScreen);
+
 extern _X_EXPORT Bool RROutputSetNonDesktop(RROutputPtr output, Bool non_desktop);
 
 extern _X_EXPORT CARD16