vout: fix uninitialized pointer dereference

A failing vout_Request() on a re-used vout caused to save an invalid vout
pointer.

This also fixes the following warning: ‘vout’ may be used uninitialized in this
function [-Wmaybe-uninitialized] input_resource_PutVout(p_resource, vout);

Regression from 4586ffaf

src/input/resource.c

@@ -401,7 +401,7 @@ vout_thread_t *input_resource_GetVout(input_resource_t *p_resource,
 
     if (vout_Request(cfg, p_resource->p_input)) {
         vlc_mutex_unlock(&p_resource->lock);
-        input_resource_PutVout(p_resource, vout);
+        input_resource_PutVout(p_resource, cfg->vout);
         return NULL;
     }