cryptonote_protocol: print peer versions when unexpected

also avoid integer underflow on zero height

src/cryptonote_protocol/cryptonote_protocol_handler.inl

@@ -266,13 +266,17 @@ namespace cryptonote
       return true;
 
     // from v6, if the peer advertises a top block version, reject if it's not what it should be (will only work if no voting)
-    const uint8_t version = m_core.get_ideal_hard_fork_version(hshd.current_height - 1);
-    if (version >= 6 && version != hshd.top_version)
+    if (hshd.current_height > 0)
     {
-      if (version < hshd.top_version)
-        MCLOG_RED(el::Level::Warning, "global", context << " peer claims higher version that we think - we may be forked from the network and a software upgrade may be needed");
-      LOG_DEBUG_CC(context, "Ignoring due to wrong top version for block " << (hshd.current_height - 1) << ": " << (unsigned)hshd.top_version << ", expected " << (unsigned)version);
-      return false;
+      const uint8_t version = m_core.get_ideal_hard_fork_version(hshd.current_height - 1);
+      if (version >= 6 && version != hshd.top_version)
+      {
+        if (version < hshd.top_version)
+          MCLOG_RED(el::Level::Warning, "global", context << " peer claims higher version that we think (" <<
+              (unsigned)hshd.top_version << " for " << (hshd.current_height - 1) << "instead of " << (unsigned)version <<
+              ") - we may be forked from the network and a software upgrade may be needed");
+        return false;
+      }
     }
 
     context.m_remote_blockchain_height = hshd.current_height;