Ensure crash in commit/rollback does not try twice

It is possible that if during the rollback or commit command
that there may be a disk error that will cause SQLite to return
an error.  When that happens we must not attempt to rollback again.

This was seen when running multi-threaded and a bug in some code
resulted in the SQLite file descripter being closed in the middle of
a transaction.

include/sqlite/transaction.hpp

@@ -100,10 +100,17 @@ namespace sqlite{
           * \return \c true if transaction is still active, \c false otherwise
           */
         bool isActive() const { return m_isActive; }
+        /** \brief Allow to check if transaction handled by this object is
+          * currently in the middle of a COMMIT/Rollback operation.  It is used
+          * for the handling of exceptions during commit/rollback operations.
+          * \return \c true if transaction is committing/rolling back, \c false otherwise
+          */
+        bool isEnding() const { return m_isEnding; }
     private:
         void exec(std::string const &);
         connection & m_con;
         bool m_isActive; ///< if \c true there is a transaction currently opened
+        bool m_isEnding; ///< if \c true there is a transaction is currently ending
     };
 }
 

src/sqlite/transaction.cpp

@@ -42,8 +42,18 @@ namespace sqlite{
     }
 
     transaction::~transaction(){
+        // when the transaction is stuck ending, the commit/rollback failed
+        // and we don't want to take further action, we must assume there is
+        // nothing we can do.
+        if (m_isEnding) {
+            return;
+        }
         if (m_isActive) {
-            rollback();
+            try {
+                rollback();
+            } catch (...) {
+                // We can't recover in the destructor, hope for the best and continue.
+            }
         }
     }
 
@@ -61,17 +71,23 @@ namespace sqlite{
     }
 
     void transaction::end(){
+        m_isEnding = true;
         exec("END TRANSACTION");
+        m_isEnding = false;
         m_isActive = false;
     }
 
     void transaction::commit(){
+        m_isEnding = true;
         exec("COMMIT TRANSACTION");
+        m_isEnding = false;
         m_isActive = false;
     }
 
     void transaction::rollback(){
+        m_isEnding = true;
         exec("ROLLBACK TRANSACTION");
+        m_isEnding = false;
         m_isActive = false;
     }