miext: damage: protect against NULL screen priv or funcs

Protect against SEGFAULT in cases where per-screen damage private
hasn't been initialized yet or already destroyed, or function pointers
not implemented.

Signed-off-by: Enrico Weigelt, metux IT consult <info@metux.net>

miext/damage/damage.c

@@ -1714,7 +1714,8 @@ DamageCreate(DamageReportFunc damageReport,
     pDamage->damageDestroy = damageDestroy;
     pDamage->pScreen = pScreen;
 
-    (*pScrPriv->funcs.Create) (pDamage);
+    if (pScrPriv && pScrPriv->funcs.Create)
+        pScrPriv->funcs.Create(pDamage);
 
     return pDamage;
 }
@@ -1755,7 +1756,8 @@ DamageRegister(DrawablePtr pDrawable, DamagePtr pDamage)
         pDamage->isWindow = FALSE;
     pDamage->pDrawable = pDrawable;
     damageInsertDamage(getDrawableDamageRef(pDrawable), pDamage);
-    (*pScrPriv->funcs.Register) (pDrawable, pDamage);
+    if (pScrPriv && pScrPriv->funcs.Register)
+        pScrPriv->funcs.Register(pDrawable, pDamage);
 }
 
 void
@@ -1774,7 +1776,10 @@ DamageUnregister(DamagePtr pDamage)
 
     damageScrPriv(pScreen);
 
-    (*pScrPriv->funcs.Unregister) (pDrawable, pDamage);
+    if (pScrPriv && pScrPriv->funcs.Unregister)
+        pScrPriv->funcs.Unregister(pDrawable, pDamage);
+    else
+        miDamageUnregister(pDrawable, pDamage);
 
     if (pDrawable->type == DRAWABLE_WINDOW) {
         WindowPtr pWindow = (WindowPtr) pDrawable;
@@ -1817,7 +1822,9 @@ DamageDestroy(DamagePtr pDamage)
 
     if (pDamage->damageDestroy)
         (*pDamage->damageDestroy) (pDamage, pDamage->closure);
-    (*pScrPriv->funcs.Destroy) (pDamage);
+
+    if (pScrPriv && pScrPriv->funcs.Destroy)
+        pScrPriv->funcs.Destroy(pDamage);
     RegionUninit(&pDamage->damage);
     RegionUninit(&pDamage->pendingDamage);
     free(pDamage);