Use std::unique_ptr for pdf objects

common/comic.h

@@ -165,11 +165,11 @@ class PDFComic : public Comic
 private:
 // pdf
 #if defined Q_OS_MAC && defined USE_PDFKIT
-    MacOSXPDFComic *pdfComic;
+    std::unique_ptr<MacOSXPDFComic> pdfComic;
 #elif defined USE_PDFIUM
-    PdfiumComic *pdfComic;
+    std::unique_ptr<PdfiumComic> pdfComic;
 #else
-    Poppler::Document *pdfComic;
+    std::unique_ptr<Poppler::Document> pdfComic;
 #endif
     void renderPage(int page);
     // void run();