wined3d: Don't free backends if they're not created yet.

This would crash if CreateAdditionalSwapChain() failed.

dlls/wined3d/device.c

diff --git a/dlls/wined3d/device.c b/dlls/wined3d/device.c
index e1e01e2..69a7642 100644
--- a/dlls/wined3d/device.c
+++ b/dlls/wined3d/device.c
@@ -2259,9 +2259,15 @@
         IWineD3DStateBlock_Release((IWineD3DStateBlock *) This->stateBlock);
         This->stateBlock = NULL;
     }
-    This->blitter->free_private(iface);
-    This->frag_pipe->free_private(iface);
-    This->shader_backend->shader_free_private(iface);
+    if (This->blit_priv) {
+        This->blitter->free_private(iface);
+    }
+    if (This->fragment_priv) {
+        This->frag_pipe->free_private(iface);
+    }
+    if (This->shader_priv) {
+        This->shader_backend->shader_free_private(iface);
+    }
     return hr;
 }