CLI: optional HEIF support

src/img2pdf.py

@@ -4224,6 +4224,17 @@ and left/right, respectively. It is not possible to specify asymmetric borders.
     if args.verbose:
         logging.basicConfig(level=logging.DEBUG)
 
+    # optional support for HEIF/HEIC via Pillow plugin
+    # only for the CLI to let library users choose on their own
+    # https://gitlab.mister-muffin.de/josch/img2pdf/issues/105
+    # https://github.com/python-pillow/Pillow/issues/2806
+    try:
+        import pillow_heif
+    except ImportError:
+        pass
+    else:
+        pillow_heif.register_heif_opener()
+
     if args.pillow_limit_break:
         Image.MAX_IMAGE_PIXELS = None