fix dgoss edit return code (#805)

Before dgoss edit returned a 1 return code if GOSS_VARS was unset
but the command was valid.
By refactoring the test of GOSS_VARS with the if clause, dgoss edit
command returns the return code of get_docker_file function.

Signed-off-by: Andrea Grillo <andrea.grillo96@live.com>
Co-authored-by: Ahmed Elsabbahy <aelsabbahy@users.noreply.github.com>

extras/dgoss/dgoss

@@ -125,7 +125,9 @@ case "$1" in
         $CONTAINER_RUNTIME exec -it "$id" sh -c 'cd /goss; PATH="/goss:$PATH" exec sh'
         get_docker_file "$id" "/goss/goss.yaml" "${GOSS_FILES_PATH}/${GOSS_FILE:-goss.yaml}"
         get_docker_file "$id" "/goss/goss_wait.yaml" "${GOSS_FILES_PATH}/goss_wait.yaml"
-        [[ ! -z "${GOSS_VARS}" ]] && get_docker_file "$id" "/goss/${GOSS_VARS}" "${GOSS_FILES_PATH}/${GOSS_VARS}"
+        if [[ ! -z "${GOSS_VARS}" ]]; then
+            get_docker_file "$id" "/goss/${GOSS_VARS}" "${GOSS_FILES_PATH}/${GOSS_VARS}"
+        fi
         ;;
     *)
         error "$USAGE"