Launcher: fix loading of mcicon (#1779)

Co-authored-by: black-sliver <59490463+black-sliver@users.noreply.github.com>

setup.py

@@ -157,11 +157,22 @@ build_arch = build_platform.split('-')[-1] if '-' in build_platform else platfor
 
 
 # see Launcher.py on how to add scripts to setup.py
+def resolve_icon(icon_name: str):
+    base_path = icon_paths[icon_name]
+    if is_windows:
+        path, extension = os.path.splitext(base_path)
+        ico_file = path + ".ico"
+        assert os.path.exists(ico_file), f"ico counterpart of {base_path} should exist."
+        return ico_file
+    else:
+        return base_path
+
+
 exes = [
     cx_Freeze.Executable(
         script=f'{c.script_name}.py',
         target_name=c.frozen_name + (".exe" if is_windows else ""),
-        icon=icon_paths[c.icon],
+        icon=resolve_icon(c.icon),
         base="Win32GUI" if is_windows and not c.cli else None
     ) for c in components if c.script_name and c.frozen_name
 ]