imgconverter: allow icons up to 2048x2048

Recently some applications ships with large icons like 1024x1024
(Signal-desktop for example). To not degrade any fancy HiDPI 8K
experience, allow for that, instead of downscaling.
The max icon size is only anti-DoS protection anyway.

imgconverter/qubesimgconverter/__init__.py

@@ -44,7 +44,7 @@ MAX_HEIGHT = 5120
 # current max raster icon size in hicolor theme is 256 as of 2013/fedora-18
 # beyond that one probably shall use scalable icons
 # (SVG is currently unsupported)
-ICON_MAXSIZE = 512
+ICON_MAXSIZE = 2048
 
 # header consists of two decimal numbers, SPC and LF
 re_imghdr = re.compile(br'^\d+ \d+\n$')