[PATCH] dri2: Fix detection of wrong prime_id in GetScreenPrime.

[Michal Srb]

Checking the iterating variable ("slave") against null can not detect if the
xorg_list_for_each_entry finished without break being invoked - slave variable
will be always non-null. This caused segfault whenever someone tried to use
DRI_PRIME with incorrect id while having at least one render offloading slave
configured.

Restructurize the GetScreenPrime to work as expected.

diff --git a/hw/xfree86/dri2/dri2.c b/hw/xfree86/dri2/dri2.c
index 729a323..5b2c662 100644
--- a/hw/xfree86/dri2/dri2.c
+++ b/hw/xfree86/dri2/dri2.c
@@ -156,11 +156,9 @@ GetScreenPrime(ScreenPtr master, int prime_id)
 
         ds = DRI2GetScreen(slave);
         if (ds->prime_id == prime_id)
-            break;
+            return slave;
     }
-    if (!slave)
-        return master;
-    return slave;
+    return master;
 }
 
 static DRI2ScreenPtr