fix: ignore ping command in connection keepalive logic (#480)

Fixes #479

### Motivation

The current keepalive logic is too lenient – merely receiving ping commands can keep the connection alive.

### Modifications

Ignore ping command in connection keepalive logic.

(cherry picked from commit f37bf92)

Author: erobot

lib/ClientConnection.cc

@@ -924,7 +924,9 @@ void ClientConnection::handleIncomingCommand(BaseCommand& incomingCmd) {
         case Ready: {
             // Since we are receiving data from the connection, we are assuming that for now the
             // connection is still working well.
-            havePendingPingRequest_ = false;
+            if (incomingCmd.type() != BaseCommand::PING) {
+                havePendingPingRequest_ = false;
+            }
 
             // Handle normal commands
             switch (incomingCmd.type()) {