Deep copy the BIO's backing memory for the QSslKey

This doesn't appear to be a problem in practice, but the docs don't say
that Qt couldn't retain this QByteArray for later, which would result in
a UAF with the current code.

app/backend/identitymanager.cpp

@@ -170,7 +170,7 @@ IdentityManager::getSslKey()
 
         BUF_MEM* mem;
         BIO_get_mem_ptr(bio, &mem);
-        m_CachedSslKey = QSslKey(QByteArray::fromRawData(mem->data, (int)mem->length), QSsl::Rsa);
+        m_CachedSslKey = QSslKey(QByteArray(mem->data, (int)mem->length), QSsl::Rsa);
 
         BIO_free(bio);
         EVP_PKEY_free(pk);