Fix TomcatHeadersAdapter.clear()

This commit fixes a regression introduced in TomcatHeadersAdapter in
conjunction with gh-33916.

Closes gh-34092

spring-web/src/main/java/org/springframework/http/server/reactive/TomcatHeadersAdapter.java

@@ -163,8 +163,8 @@ class TomcatHeadersAdapter implements MultiValueMap<String, String> {
 
 	@Override
 	public void clear() {
-		for (int i = 0 ; i < this.headers.size(); i++) {
-			this.headers.removeHeader(i);
+		while (this.headers.size() > 0) {
+			this.headers.removeHeader(0);
 		}
 	}
 

spring-web/src/test/java/org/springframework/http/server/reactive/TomcatHeadersAdapterTests.java

@@ -0,0 +1,41 @@
+/*
+ * Copyright 2002-2024 the original author or authors.
+ *
+ * Licensed under the Apache License, Version 2.0 (the "License");
+ * you may not use this file except in compliance with the License.
+ * You may obtain a copy of the License at
+ *
+ *      https://www.apache.org/licenses/LICENSE-2.0
+ *
+ * Unless required by applicable law or agreed to in writing, software
+ * distributed under the License is distributed on an "AS IS" BASIS,
+ * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+ * See the License for the specific language governing permissions and
+ * limitations under the License.
+ */
+
+package org.springframework.http.server.reactive;
+
+import org.apache.tomcat.util.http.MimeHeaders;
+import org.junit.jupiter.api.Test;
+
+import static org.assertj.core.api.Assertions.assertThat;
+
+/**
+ * Tests for {@link TomcatHeadersAdapter}.
+ *
+ * @author Johnny Lim
+ */
+class TomcatHeadersAdapterTests {
+
+	@Test
+	void clear() {
+		MimeHeaders mimeHeaders = new MimeHeaders();
+		TomcatHeadersAdapter adapter = new TomcatHeadersAdapter(mimeHeaders);
+		adapter.add("key1", "value1");
+		adapter.add("key2", "value2");
+		adapter.clear();
+		assertThat(adapter).isEmpty();
+	}
+
+}