testutilsxen: error out on initialization failure

libxlDriverConfigNew can possibly fail on wrong
firmware values (unlikely) or on failure to create
the log directory (possible if you're debugging
tests with VIR_FILE_ACCESS)
Signed-off-by: NJán Tomko <jtomko@redhat.com>
Fixes: 4a4132b4Reviewed-by: NJim Fehlig <jfehlig@suse.com>

tests/testutilsxen.c

@@ -94,7 +94,8 @@ libxlDriverPrivatePtr testXLInitDriver(void)
         return NULL;
     }
 
-    driver->config = libxlDriverConfigNew();
+    if (!(driver->config = libxlDriverConfigNew()))
+        return NULL;
 
     driver->config->caps = testXLInitCaps();