service/vi: Factor out scaling mode conversions from the IPC function itself

Avoids entangling the IPC buffer appending with the actual operation of
converting the scaling values over. This also inserts the proper error
handling for invalid scaling values.

src/core/hle/service/vi/vi.cpp

@@ -1003,7 +1003,7 @@ private:
         const u64 unknown = rp.Pop<u64>();
 
         LOG_DEBUG(Service_VI, "called. scaling_mode=0x{:08X}, unknown=0x{:016X}",
-                    static_cast<u32>(scaling_mode), unknown);
+                  static_cast<u32>(scaling_mode), unknown);
 
         IPC::ResponseBuilder rb{ctx, 2};
 
@@ -1102,31 +1102,35 @@ private:
 
     void ConvertScalingMode(Kernel::HLERequestContext& ctx) {
         IPC::RequestParser rp{ctx};
-        auto mode = rp.PopEnum<NintendoScaleMode>();
+        const auto mode = rp.PopEnum<NintendoScaleMode>();
         LOG_DEBUG(Service_VI, "called mode={}", static_cast<u32>(mode));
 
-        IPC::ResponseBuilder rb{ctx, 4};
-        rb.Push(RESULT_SUCCESS);
+        const auto converted_mode = ConvertScalingModeImpl(mode);
+
+        if (converted_mode.Succeeded()) {
+            IPC::ResponseBuilder rb{ctx, 4};
+            rb.Push(RESULT_SUCCESS);
+            rb.PushEnum(*converted_mode);
+        } else {
+            IPC::ResponseBuilder rb{ctx, 2};
+            rb.Push(converted_mode.Code());
+        }
+    }
+
+    static ResultVal<ConvertedScaleMode> ConvertScalingModeImpl(NintendoScaleMode mode) {
         switch (mode) {
         case NintendoScaleMode::None:
-            rb.PushEnum(ConvertedScaleMode::None);
-            break;
+            return MakeResult(ConvertedScaleMode::None);
         case NintendoScaleMode::Freeze:
-            rb.PushEnum(ConvertedScaleMode::Freeze);
-            break;
+            return MakeResult(ConvertedScaleMode::Freeze);
         case NintendoScaleMode::ScaleToWindow:
-            rb.PushEnum(ConvertedScaleMode::ScaleToWindow);
-            break;
+            return MakeResult(ConvertedScaleMode::ScaleToWindow);
         case NintendoScaleMode::Crop:
-            rb.PushEnum(ConvertedScaleMode::Crop);
-            break;
+            return MakeResult(ConvertedScaleMode::Crop);
         case NintendoScaleMode::NoCrop:
-            rb.PushEnum(ConvertedScaleMode::NoCrop);
-            break;
+            return MakeResult(ConvertedScaleMode::NoCrop);
         default:
-            UNIMPLEMENTED_MSG("Unknown scaling mode {}", static_cast<u32>(mode));
-            rb.PushEnum(ConvertedScaleMode::None);
-            break;
+            return ERR_OPERATION_FAILED;
         }
     }