HTTPCLIENT-2361: Tolerate multiple Cookie headers added by the caller

Author: ok2c

httpclient5/src/main/java/org/apache/hc/client5/http/protocol/RequestAddCookies.java

@@ -91,9 +91,8 @@ public void process(final HttpRequest request, final EntityDetails entity, final
             return;
         }
 
-        final Header cookieHeader = request.getHeader(HttpHeaders.COOKIE);
         // Check if a Cookie header is already present
-        if (cookieHeader != null) {
+        if (request.containsHeader(HttpHeaders.COOKIE)) {
             if (LOG.isDebugEnabled()) {
                 LOG.debug("Skipping cookie addition, Cookie header already present in the request");
             }