Fix compile warning with --cfg require_route_graph_test

Author: TheBlueMatt

lightning/src/routing/router.rs

@@ -3850,7 +3850,8 @@ mod tests {
 				File::open(path)
 			});
 		#[cfg(require_route_graph_test)]
-		return Ok(res.expect("Didn't have route graph and was configured to require it"));
+		Ok(res.expect("Didn't have route graph and was configured to require it"))
+		#[cfg(not(require_route_graph_test))]
 		res
 	}