Convert icon to RGB mode before conversion

Some JPEG files appear to use a non-RGB mode, causing a crash when
trying to save the image without converting it first.

Also default to using the original icon if it can't be resized for some
reason.

Fixes #246

CHANGELOG.md

@@ -4,6 +4,10 @@ All notable changes to this project will be documented in this file.
 
 The format is based on [Keep a Changelog](https://keepachangelog.com/en/1.0.0/).
 
+## [Unreleased]
+### Fixed
+ - Fix crash caused by custom app icons with non-RGB mode
+
 ## [1.10.4] - 2023-08-26
 ### Fixed
  - Fix crash caused by the Steam shortcut configuration file containing extra data after the VDF section

src/protontricks/gui.py

@@ -100,9 +100,16 @@ def _get_appid2icon(steam_apps, steam_path):
                         "App icon %s has unusual size, resizing",
                         original_icon_path
                     )
-                    resized_img = img.resize(APP_ICON_SIZE)
-                    resized_img.save(icon_cache_path)
-                    final_icon_path = icon_cache_path
+                    try:
+                        resized_img = img.resize(APP_ICON_SIZE).convert("RGB")
+                        resized_img.save(icon_cache_path)
+                        final_icon_path = icon_cache_path
+                    except Exception:
+                        logger.warning(
+                            "Could not resize %s, ignoring",
+                            original_icon_path,
+                            exc_info=True
+                        )
 
         appid2icon[app.appid] = final_icon_path