Fix coverity issues column_family, compaction_db/iterator

Summary:
db/column_family.h :
79  ColumnFamilyHandleInternal()

CID 1322806 (#1 of 1): Uninitialized pointer field (UNINIT_CTOR)
2. uninit_member: Non-static class member internal_cfd_ is not initialized in this constructor nor in any functions that it calls.
 80      : ColumnFamilyHandleImpl(nullptr, nullptr, nullptr) {}

db/compacted_db_impl.cc:
 18CompactedDBImpl::CompactedDBImpl(
 19  const DBOptions& options, const std::string& dbname)
 20  : DBImpl(options, dbname) {
   	2. uninit_member: Non-static class member cfd_ is not initialized in this constructor nor in any functions that it calls.
   	4. uninit_member: Non-static class member version_ is not initialized in this constructor nor in any functions that it calls.

CID 1396120 (#1 of 1): Uninitialized pointer field (UNINIT_CTOR)
6. uninit_member: Non-static class member user_comparator_ is not initialized in this constructor nor in any functions that it calls.
 21}

db/compaction_iterator.cc:
9. uninit_member: Non-static class member current_user_key_sequence_ is not initialized in this constructor nor in any functions that it calls.
11. uninit_member: Non-static class member current_user_key_snapshot_ is not initialized in this constructor nor in any functions that it calls.

CID 1419855 (#1 of 1): Uninitialized scalar field (UNINIT_CTOR)
13. uninit_member: Non-static class member current_key_committed_ is not initialized in this constructor nor in any functions that it calls.
Closes https://github.com/facebook/rocksdb/pull/3084

Differential Revision: D6172999

Pulled By: sagar0

fbshipit-source-id: 084d73393faf8022c01359cfb445807b6a782460

db/column_family.h

@@ -77,7 +77,7 @@ class ColumnFamilyHandleImpl : public ColumnFamilyHandle {
 class ColumnFamilyHandleInternal : public ColumnFamilyHandleImpl {
  public:
   ColumnFamilyHandleInternal()
-      : ColumnFamilyHandleImpl(nullptr, nullptr, nullptr) {}
+      : ColumnFamilyHandleImpl(nullptr, nullptr, nullptr), internal_cfd_(nullptr) {}
 
   void SetCFD(ColumnFamilyData* _cfd) { internal_cfd_ = _cfd; }
   virtual ColumnFamilyData* cfd() const override { return internal_cfd_; }

db/compacted_db_impl.cc

@@ -17,7 +17,8 @@ extern bool SaveValue(void* arg, const ParsedInternalKey& parsed_key,
 
 CompactedDBImpl::CompactedDBImpl(
   const DBOptions& options, const std::string& dbname)
-  : DBImpl(options, dbname) {
+  : DBImpl(options, dbname), cfd_(nullptr), version_(nullptr),
+    user_comparator_(nullptr) {
 }
 
 CompactedDBImpl::~CompactedDBImpl() {

db/compaction_iterator.cc

@@ -80,7 +80,10 @@ CompactionIterator::CompactionIterator(
 #endif  // ROCKSDB_LITE
       shutting_down_(shutting_down),
       ignore_snapshots_(false),
-      merge_out_iter_(merge_helper_) {
+      current_user_key_sequence_(0),
+      current_user_key_snapshot_(0),
+      merge_out_iter_(merge_helper_),
+      current_key_committed_(false) {
   assert(compaction_filter_ == nullptr || compaction_ != nullptr);
   bottommost_level_ =
       compaction_ == nullptr ? false : compaction_->bottommost_level();