Stop emitting errors when there is no previous tag, use the first commit on the branch

gitversion.sh

@@ -13,7 +13,11 @@ REBUILDING=0
 SHA1=$(git rev-parse HEAD)
 TAG=$(git log --tags --simplify-by-decoration --pretty="format:%D" | grep -Eo "${VERSIONERS_TAGBASE},[0-9\.]+,[0-9]+" 2>/dev/null | head -n 1)
 BUILD=0
+if [[ "$TAG" != "" ]]; then
     TAGSHA=$(git rev-list $TAG | head -n 1)
+else
+    TAGSHA=$(git rev-list --max-parents=0 HEAD)
+fi
 CHANGELOG="$(git log --format="format:$LOGSPEC" ${TAGSHA}..HEAD)"
 if [ "$TAG" == "" ]; then
     BUILD=0