fix possible memory leaks in CWallet::EncryptWallet

- add missing deletes for pwalletdbEncryption
- add an assert before trying to reserve memory for pwalletdbEncryption
- add a destructor to CWallet, which ensures deletion of
  pwalletdbEncryption on object destruction

src/wallet.cpp

@@ -426,17 +426,25 @@ bool CWallet::EncryptWallet(const SecureString& strWalletPassphrase)
         mapMasterKeys[++nMasterKeyMaxID] = kMasterKey;
         if (fFileBacked)
         {
+            assert(!pwalletdbEncryption);
             pwalletdbEncryption = new CWalletDB(strWalletFile);
-            if (!pwalletdbEncryption->TxnBegin())
+            if (!pwalletdbEncryption->TxnBegin()) {
+                delete pwalletdbEncryption;
+                pwalletdbEncryption = NULL;
                 return false;
+            }
             pwalletdbEncryption->WriteMasterKey(nMasterKeyMaxID, kMasterKey);
         }
 
         if (!EncryptKeys(vMasterKey))
         {
-            if (fFileBacked)
+            if (fFileBacked) {
                 pwalletdbEncryption->TxnAbort();
-            exit(1); //We now probably have half of our keys encrypted in memory, and half not...die and let the user reload their unencrypted wallet.
+                delete pwalletdbEncryption;
+            }
+            // We now probably have half of our keys encrypted in memory, and half not...
+            // die and let the user reload their unencrypted wallet.
+            exit(1);
         }
 
         // Encryption was introduced in version 0.4.0
@@ -444,8 +452,12 @@ bool CWallet::EncryptWallet(const SecureString& strWalletPassphrase)
 
         if (fFileBacked)
         {
-            if (!pwalletdbEncryption->TxnCommit())
-                exit(1); //We now have keys encrypted in memory, but no on disk...die to avoid confusion and let the user reload their unencrypted wallet.
+            if (!pwalletdbEncryption->TxnCommit()) {
+                delete pwalletdbEncryption;
+                // We now have keys encrypted in memory, but no on disk...
+                // die to avoid confusion and let the user reload their unencrypted wallet.
+                exit(1);
+            }
 
             delete pwalletdbEncryption;
             pwalletdbEncryption = NULL;

src/wallet.h

@@ -143,6 +143,7 @@ public:
     {
         SetNull();
     }
+
     CWallet(std::string strWalletFileIn)
     {
         SetNull();
@@ -150,6 +151,13 @@ public:
         strWalletFile = strWalletFileIn;
         fFileBacked = true;
     }
+
+    ~CWallet()
+    {
+        delete pwalletdbEncryption;
+        pwalletdbEncryption = NULL;
+    }
+
     void SetNull()
     {
         nWalletVersion = FEATURE_BASE;