blockchain: fix off by one getting blocks

src/cryptonote_core/blockchain.cpp

@@ -1444,7 +1444,7 @@ bool Blockchain::get_blocks(uint64_t start_offset, size_t count, std::list<std::
 {
   LOG_PRINT_L3("Blockchain::" << __func__);
   CRITICAL_REGION_LOCAL(m_blockchain_lock);
-  if(start_offset > m_db->height())
+  if(start_offset >= m_db->height())
     return false;
 
   if (!get_blocks(start_offset, count, blocks))
@@ -1466,7 +1466,7 @@ bool Blockchain::get_blocks(uint64_t start_offset, size_t count, std::list<std::
 {
   LOG_PRINT_L3("Blockchain::" << __func__);
   CRITICAL_REGION_LOCAL(m_blockchain_lock);
-  if(start_offset > m_db->height())
+  if(start_offset >= m_db->height())
     return false;
 
   for(size_t i = start_offset; i < start_offset + count && i < m_db->height();i++)