VR: Fix render target manager failures on 5.6

Author: praydog

src/mods/vr/FFakeStereoRenderingHook.cpp

@@ -885,6 +885,7 @@ bool FFakeStereoRenderingHook::standard_fake_stereo_hook(uintptr_t vtable) {
 
                     // On UE5.5+ FFakeStereoRendering has a valid GetRenderTargetManager that doesn't return null.
                     if (!is_4_18_or_lower && func(og_vtable.data(), nullptr, nullptr, nullptr) == (IStereoRenderTargetManager*)&og_vtable[sizeof(void*)]) {
+                        m_uses_old_rendertarget_manager = false; // nope
                         SPDLOG_INFO("Found UE5.5+ variant of GetRenderTargetManager function at index {}", render_target_manager_vtable_index);
                         SPDLOG_INFO("GetRenderTargetManager function at index {} appears to be valid.", render_target_manager_vtable_index);
                         break;