Make SafeDbt DB_DBT_MALLOC on default initialization

If we're constructing the SafeDbt without provided data, it is always malloced,
so that is the case we expose.

Also run clang-format.

src/wallet/db.cpp

@@ -247,12 +247,12 @@ BerkeleyEnvironment::VerifyResult BerkeleyEnvironment::Verify(const std::string&
     return (fRecovered ? VerifyResult::RECOVER_OK : VerifyResult::RECOVER_FAIL);
 }
 
-BerkeleyBatch::SafeDbt::SafeDbt(u_int32_t flags)
+BerkeleyBatch::SafeDbt::SafeDbt()
 {
-    m_dbt.set_flags(flags);
+    m_dbt.set_flags(DB_DBT_MALLOC);
 }
 
-BerkeleyBatch::SafeDbt::SafeDbt(void *data, size_t size)
+BerkeleyBatch::SafeDbt::SafeDbt(void* data, size_t size)
     : m_dbt(data, size)
 {
 }

src/wallet/db.h

@@ -170,13 +170,15 @@ class BerkeleyDatabase
 class BerkeleyBatch
 {
     /** RAII class that automatically cleanses its data on destruction */
-    class SafeDbt final {
+    class SafeDbt final
+    {
         Dbt m_dbt;
 
     public:
-        // construct Dbt with data or flags
-        SafeDbt(u_int32_t flags = 0);
-        SafeDbt(void *data, size_t size);
+        // construct Dbt with internally-managed data
+        SafeDbt();
+        // construct Dbt with provided data
+        SafeDbt(void* data, size_t size);
         ~SafeDbt();
 
         // delegate to Dbt
@@ -227,7 +229,7 @@ class BerkeleyBatch
         SafeDbt datKey(ssKey.data(), ssKey.size());
 
         // Read
-        SafeDbt datValue(DB_DBT_MALLOC);
+        SafeDbt datValue;
         int ret = pdb->get(activeTxn, datKey, datValue, 0);
         bool success = false;
         if (datValue.get_data() != nullptr) {
@@ -318,8 +320,8 @@ class BerkeleyBatch
     int ReadAtCursor(Dbc* pcursor, CDataStream& ssKey, CDataStream& ssValue)
     {
         // Read at cursor
-        SafeDbt datKey(DB_DBT_MALLOC);
-        SafeDbt datValue(DB_DBT_MALLOC);
+        SafeDbt datKey;
+        SafeDbt datValue;
         int ret = pcursor->get(datKey, datValue, DB_NEXT);
         if (ret != 0)
             return ret;