autocf: determine mod file availability from downloadUrl (#2046)

Author: itzg

Dockerfile

@@ -46,7 +46,7 @@ RUN easy-add --var os=${TARGETOS} --var arch=${TARGETARCH}${TARGETVARIANT} \
   --var version=0.1.1 --var app=maven-metadata-release --file {{.app}} \
   --from https://github.com/itzg/{{.app}}/releases/download/{{.version}}/{{.app}}_{{.version}}_{{.os}}_{{.arch}}.tar.gz
 
-ARG MC_HELPER_VERSION=1.25.20
+ARG MC_HELPER_VERSION=1.25.21
 ARG MC_HELPER_BASE_URL=https://github.com/itzg/mc-image-helper/releases/download/${MC_HELPER_VERSION}
 RUN curl -fsSL ${MC_HELPER_BASE_URL}/mc-image-helper-${MC_HELPER_VERSION}.tgz \
   | tar -C /usr/share -zxf - \