Fix memory leak of CredHandle in wintls.c

[Copilot]

hssl_ctx_init allocates a CredHandle via malloc but hssl_ctx_free only calls FreeCredentialsHandle without freeing the backing memory.

• Added free(ssl_ctx) after FreeCredentialsHandle in hssl_ctx_free

void hssl_ctx_free(hssl_ctx_t ssl_ctx)
{
    SECURITY_STATUS sec_status = FreeCredentialsHandle(ssl_ctx);
    if (sec_status != SEC_E_OK) {
        printe("free_cred_handle FreeCredentialsHandle %d\n", sec_status);
    }
    free(ssl_ctx);
}

Original prompt

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This section details on the original issue you should resolve

<issue_title>疑似内存泄漏</issue_title>
<issue_description>首先感谢作者开源了这么好的一个库,使用过程中发现好像有个内存泄漏的地方.麻烦看看
https://github.com/ithewei/libhv/blob/master/ssl/wintls.c#L160

    hCred = (CredHandle*)malloc(sizeof(CredHandle));
    if (hCred == NULL) {
        return NULL;
    }

这里malloc了一个CredHandle* hCred 在 hssl_ctx_free 中好像没有free
https://github.com/ithewei/libhv/blob/master/ssl/wintls.c#L183

void hssl_ctx_free(hssl_ctx_t ssl_ctx)
{
    SECURITY_STATUS sec_status = FreeCredentialsHandle(ssl_ctx);
    if (sec_status != SEC_E_OK) {
        printe("free_cred_handle FreeCredentialsHandle %d\n", sec_status);
    }
}

这应该会导致内存泄漏吧</issue_description>

Comments on the Issue (you are @copilot in this section)

• Fixes 疑似内存泄漏 #802

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