stop agent operations can cause the program to crash

[tercel]

packages/core/runtime.ts:
stop() can cause the program to crash.

change the below code is work well.

// it doesn't have a strict interface specification, and some don't have STOP methods
if (c && c?.stop) {
    c.stop();
} else {
    elizaLogger.log("client stop skip,", cStr, this.character.name);
}