[UI] Remove MAX_PATH limit from WM_DROPFILES

Also required const-ifying a file drop message.

src/xenia/app/emulator_window.cc

@@ -291,9 +291,8 @@ bool EmulatorWindow::Initialize() {
   return true;
 }
 
-void EmulatorWindow::FileDrop(wchar_t* filename) {
-  std::wstring path = filename;
-  auto result = emulator_->LaunchPath(path);
+void EmulatorWindow::FileDrop(const wchar_t* filename) {
+  auto result = emulator_->LaunchPath(filename);
   if (XFAILED(result)) {
     // TODO: Display a message box.
     XELOGE("Failed to launch target: %.8X", result);

src/xenia/app/emulator_window.h

@@ -43,7 +43,7 @@ class EmulatorWindow {
 
   bool Initialize();
 
-  void FileDrop(wchar_t* filename);
+  void FileDrop(const wchar_t* filename);
   void FileOpen();
   void FileClose();
   void ShowContentDirectory();

src/xenia/ui/ui_event.h

@@ -28,14 +28,14 @@ class UIEvent {
 
 class FileDropEvent : public UIEvent {
  public:
-  FileDropEvent(Window* target, wchar_t* filename)
+  FileDropEvent(Window* target, const wchar_t* filename)
       : UIEvent(target), filename_(filename) {}
   ~FileDropEvent() override = default;
 
-  wchar_t* filename() const { return filename_; }
+  const wchar_t* filename() const { return filename_; }
 
  private:
-  wchar_t* filename_ = nullptr;
+  const wchar_t* filename_ = nullptr;
 };
 
 class KeyEvent : public UIEvent {

src/xenia/ui/window_win.cc

@@ -492,16 +492,19 @@ LRESULT Win32Window::WndProc(HWND hWnd, UINT message, WPARAM wParam,
 
   switch (message) {
     case WM_DROPFILES: {
-      TCHAR lpszFile[MAX_PATH] = {0};
-      UINT uFiles = 0;
-      HDROP hDrop = (HDROP)wParam;
-      // Get number of files dropped
-      uFiles = DragQueryFile(hDrop, -1, NULL, NULL);
+      HDROP hDrop = reinterpret_cast<HDROP>(wParam);
+      std::wstring path;
 
-      // Only getting first file dropped (other files ignored)
-      if (DragQueryFile(hDrop, 0, lpszFile, MAX_PATH)) {
-        auto e = FileDropEvent(this, lpszFile);
-        OnFileDrop(&e);
+      // Get required buffer size
+      UINT buf_size = DragQueryFileW(hDrop, 0, nullptr, 0);
+      if (buf_size > 0) {
+        path.resize(buf_size + 1);  // Give space for a null terminator
+
+        // Only getting first file dropped (other files ignored)
+        if (DragQueryFileW(hDrop, 0, &path[0], buf_size + 1)) {
+          auto e = FileDropEvent(this, path.c_str());
+          OnFileDrop(&e);
+        }
       }
 
       DragFinish(hDrop);