Defer cleanup in DefaultServerWebExchange

This commit ensures that the multipartRead flag is read in a deferred
block, and is not evaluated too early.

Closes gh-31567

spring-web/src/main/java/org/springframework/web/server/adapter/DefaultServerWebExchange.java

@@ -247,18 +247,20 @@ public Mono<MultiValueMap<String, Part>> getMultipartData() {
 
 	@Override
 	public Mono<Void> cleanupMultipart() {
-		if (this.multipartRead) {
-			return getMultipartData()
-					.onErrorResume(t -> Mono.empty()) // ignore errors reading multipart data
-					.flatMapIterable(Map::values)
-					.flatMapIterable(Function.identity())
-					.flatMap(part -> part.delete()
-									.onErrorResume(ex -> Mono.empty()))
-					.then();
-		}
-		else {
-			return Mono.empty();
-		}
+		return Mono.defer(() -> {
+			if (this.multipartRead) {
+				return getMultipartData()
+						.onErrorComplete()
+						.flatMapIterable(Map::values)
+						.flatMapIterable(Function.identity())
+						.flatMap(part -> part.delete()
+									.onErrorComplete())
+						.then();
+			}
+			else {
+				return Mono.empty();
+			}
+		});
 	}
 
 	@Override