Fix MemorySanitizer Warning by Reordering Member Variables in KafkaHandleBase

The MemorySanitizer detected a use-of-uninitialized-value issue caused by the
destruction order in KafkaHandleBase. Specifically, the deleter of the Kafka
handle accessed destroy_flags_ after it had been destroyed because destroy_flags_
was declared after handle_.

This commit reorders the member declarations so that destroy_flags_ is declared
before handle_. The constructor's initializer list is also updated accordingly
to match the new declaration order.

Author: filimonov

include/cppkafka/kafka_handle_base.h

@@ -391,8 +391,8 @@ class CPPKAFKA_API KafkaHandleBase {
     Configuration config_;
     TopicConfigurationMap topic_configurations_;
     std::mutex topic_configurations_mutex_;
-    HandlePtr handle_;
     int destroy_flags_;
+    HandlePtr handle_;
 };
 
 } // cppkafka

src/kafka_handle_base.cpp

@@ -48,7 +48,7 @@ namespace cppkafka {
 const milliseconds KafkaHandleBase::DEFAULT_TIMEOUT{1000};
 
 KafkaHandleBase::KafkaHandleBase(Configuration config) 
-: timeout_ms_(DEFAULT_TIMEOUT), config_(move(config)), handle_(nullptr, HandleDeleter(this)), destroy_flags_(0) {
+: timeout_ms_(DEFAULT_TIMEOUT), config_(move(config)), destroy_flags_(0), handle_(nullptr, HandleDeleter(this)) {
     auto& maybe_config = config_.get_default_topic_configuration();
     if (maybe_config) {
         maybe_config->set_as_opaque();