Fix the gamma hook landing on a garbage vtable slot

src/mods/vr/FFakeStereoRenderingHook.cpp

@@ -7278,9 +7278,18 @@ bool VRRenderTargetManager_Base::create_scene_capture() try {
         auto viewport = rtm != nullptr ? rtm->get_viewport() : nullptr;
 
         if (viewport != nullptr) {
-            return viewport->get_display_gamma();
+            const auto gamma = viewport->get_display_gamma();
+
+            // Logged because the two branches look the same on screen. A viewport reporting 2.2 and a
+            // missing viewport falling back to 2.2 give the same picture, but only this one follows the
+            // game's own gamma setting.
+            SPDLOG_INFO_ONCE("[FRenderTarget] Matching the scene capture's display gamma to the viewport's, currently {}", gamma);
+
+            return gamma;
         }
 
+        SPDLOG_WARN_ONCE("[FRenderTarget] No viewport to read the display gamma from, assuming 2.2");
+
         return 2.2f;
     };
 
@@ -7295,7 +7304,18 @@ bool VRRenderTargetManager_Base::create_scene_capture() try {
         auto& vtable = *(void**)frt;
         memcpy(original_frender_target_vtable.data(), vtable, original_frender_target_vtable.size() * sizeof(uintptr_t));
 
-        if (auto display_gamma_index = sdk::FRenderTarget::get_display_gamma_index(); display_gamma_index != 0) {
+        // has_value(), not != 0.
+        //
+        // An empty std::optional compares as less than any number, so "index != 0" was true exactly when
+        // the index had not been found. Dereferencing it wrote gamma_increase_fn at whatever slot that
+        // produced, and the vtable was swapped to that copy. In the log it shows up as a failed search
+        // with "Hooked FRenderTarget!" on the next line.
+        if (const auto display_gamma_index = sdk::FRenderTarget::get_display_gamma_index(); display_gamma_index.has_value()) {
+            if (*display_gamma_index >= original_frender_target_vtable.size()) {
+                SPDLOG_WARN("[FRenderTarget] Gamma index {} is out of range, can't hook!", *display_gamma_index);
+                return;
+            }
+
             original_frender_target_vtable[*display_gamma_index] = (uintptr_t)gamma_increase_fn;
             vtable = original_frender_target_vtable.data();
             SPDLOG_INFO("[FRenderTarget] Hooked FRenderTarget!");