Fix a possible crash in SqlTransaction::Execute(), using post-iterating on the LockedQueue instead of pre-iterating.

Thanks to click for the insight and Spp for testing.

--HG--
branch : trunk

src/shared/Database/SqlOperations.cpp

@@ -35,21 +35,32 @@ void SqlTransaction::Execute(Database *db)
 {
     const char* sql;
 
+    if (m_queue.empty())
+        return;
+
     db->DirectExecute("START TRANSACTION");
-    while (m_queue.next(sql))
+    while (!m_queue.empty())
     {
+        sql = m_queue.peek();
+        m_queue.unlock();
         if (!db->DirectExecute(sql))
         {
             free((void*)const_cast<char*>(sql));
+            m_queue.pop_front();
             db->DirectExecute("ROLLBACK");
-            while (m_queue.next(sql))
+            while (!m_queue.empty())
             {
+                sql = m_queue.peek();
+                m_queue.unlock();
                 free((void*)const_cast<char*>(sql));
+                m_queue.pop_front();
             }
+            
             return;
         }
 
         free((void*)const_cast<char*>(sql));
+        m_queue.pop_front();
     }
 
     db->DirectExecute("COMMIT");