Fix inverted vsync latch from the implicit swapchain present interval

When rtx.enableVsync is in its default WaitingForImplicitSwapchain
state, the vsync default is latched from the first swapchain's
PresentationInterval with a truthiness check. In D3D9,
D3DPRESENT_INTERVAL_IMMEDIATE (the only "present unsynchronized"
request) is 0x80000000, i.e. nonzero, so a game explicitly asking for
no vsync latches vsync On; D3DPRESENT_INTERVAL_DEFAULT (0), which
presents synchronized, latches Off. The two most common values map
backwards.

A game requesting IMMEDIATE at device creation therefore runs capped
to the display refresh with elevated present latency from boot. With
DLFG enabled the cap silently clears on the first interpolated 3D
frame (dispatchDLFG forces vsync off), which disguises the bug as
affecting menus and loading screens only; with DLFG off it persists.
The d3d9.presentInterval config cannot help because enableVsyncState
overrides the present interval at Present time.

Latch Off only for D3DPRESENT_INTERVAL_IMMEDIATE; DEFAULT, ONE and
TWO through FOUR latch On, matching D3D9 presentation interval
semantics. An explicit rtx.enableVsync user setting still takes
precedence.

Author: BinqAdams

src/d3d9/d3d9_swapchain.cpp

@@ -332,8 +332,18 @@ namespace dxvk {
 
     // NV-DXVK start: DLFG integration
     if (RtxOptions::enableVsync() == EnableVsync::WaitingForImplicitSwapchain) {
-      // save the vsync state when the first swapchain is created, to act as the default
-      RtxOptions::enableVsyncState = m_presentParams.PresentationInterval ? EnableVsync::On : EnableVsync::Off;
+      // Save the vsync state when the first swapchain is created, to act as the default.
+      // D3D9 semantics: D3DPRESENT_INTERVAL_IMMEDIATE (0x80000000) is the only
+      // "present unsynchronized" request; DEFAULT (0), ONE (1) and TWO..FOUR all
+      // present synchronized to vblank. A plain truthiness check reads IMMEDIATE
+      // (nonzero) as vsync-On and DEFAULT (zero) as vsync-Off - both inverted -
+      // which capped games that explicitly request IMMEDIATE at device creation
+      // to the display refresh until something else flipped the state (e.g.
+      // DLFG's force-vsync-off on the first interpolated 3D frame).
+      RtxOptions::enableVsyncState =
+          (m_presentParams.PresentationInterval == D3DPRESENT_INTERVAL_IMMEDIATE)
+              ? EnableVsync::Off
+              : EnableVsync::On;
     }
     // NV-DXVK end