Fix potential crash due to invalid return value

Signed-off-by: François Andriot <francois.andriot@free.fr>

src/get-carddav-report.c

@@ -86,7 +86,7 @@ static gchar* carddav_dirlist(carddav_settings* settings, carddav_error* error)
 		error->str = g_strdup("Could not initialize libcurl");
 		g_free(settings->file);
 		settings->file = NULL;
-		return TRUE;
+		return NULL;
 	}
 
 	http_header = curl_slist_append(http_header,