fix(appstore): copy dist only if directory exists

The dist/ directory is not always produced by the frontend build
(e.g. in the GitHub Actions release workflow where vite outputs the
pdf worker to js/ instead). Make the copy conditional, consistent
with the verify-appstore-package target which already uses an
if [ -d dist ] guard.

[skip ci]

Signed-off-by: Vitor Mattos <1079143+vitormattos@users.noreply.github.com>

Author: vitormattos

Makefile

@@ -107,7 +107,6 @@ appstore:
 		appinfo \
 		composer \
 		css \
-		dist \
 		img \
 		js \
 		l10n \
@@ -118,6 +117,9 @@ appstore:
 		CHANGELOG.md \
 		openapi*.json \
 		$(appstore_sign_dir)/$(app_name)
+	if [ -d dist ]; then \
+		cp -r dist $(appstore_sign_dir)/$(app_name)/; \
+	fi
 	rm -rf $(appstore_sign_dir)/$(app_name)/img/screenshot/
 	rm -rf $(appstore_sign_dir)/$(app_name)/3rdparty/.git
 	rm -rf $(appstore_sign_dir)/$(app_name)/3rdparty/.github