get_snapshot: Fix rev-list for older git versions

get_snapshot

@@ -58,7 +58,7 @@ fi
 
 if ! git_version=$(git describe --tags "${UPSTREAM_GIT_BRANCH}"); then
     # no tag yet, build arbitrary version
-    git_version=0.0.0.$(git rev-list --count "${UPSTREAM_GIT_BRANCH}").$(git rev-parse --short=12 "${UPSTREAM_GIT_BRANCH}")
+    git_version=0.0.0.$(git rev-list "${UPSTREAM_GIT_BRANCH}" | wc -l).$(git rev-parse --short=12 "${UPSTREAM_GIT_BRANCH}")
 fi
 package_version=$(echo "$git_version" | sed -e 's/^v//' -e 's/-/+/' -e 's/-/./g')
 tarball="${workdir}/${PROJECT}_${package_version}.orig.tar"