added new VP8 mode for lossless reading of RGBA, fixes failing tests

PIL/WebPImagePlugin.py

@@ -12,6 +12,7 @@ _VALID_WEBP_MODES = {
 _VP8_MODES_BY_IDENTIFIER = {
     b"VP8 ": "RGB",
     b"VP8X": "RGBA",
+    b"VP8L": "RGBA", # lossless
     }
 
 

Tests/test_file_webp.py

@@ -143,9 +143,6 @@ def test_write_lossless_rgb():
     pil_image.paste(mask, (0,0), mask)   # add some partially transparent bits.
     
     pil_image.save(temp_file, lossless=True)
-
-    # Visually checking the image in Chrome shows as expected.
-    # This is failing to read...
     
     image = Image.open(temp_file)
     image.load()