goenv-init: Fix use of optional variables that should not crash the c…

…alling shell if unset

Just use the ${variable:-} syntax to accept unset variables

libexec/goenv-init

@@ -108,14 +108,14 @@ EOL
   cat <<EOL
 export GOENV_SHELL=${shell}
 export GOENV_ROOT=${GOENV_ROOT}
-if [ -z "\${GOENV_RC_FILE}" ]; then
+if [ -z "\${GOENV_RC_FILE:-}" ]; then
   GOENV_RC_FILE="\${HOME}/.goenvrc"
 fi
-if [ -e "\${GOENV_RC_FILE}" ]; then
+if [ -e "\${GOENV_RC_FILE:-}" ]; then
   source "\${GOENV_RC_FILE}"
 fi
 if [ "\${PATH#*\$GOENV_ROOT/shims}" = "\${PATH}" ]; then
-  if [ "\${GOENV_PATH_ORDER}" = "front" ] ; then
+  if [ "\${GOENV_PATH_ORDER:-}" = "front" ] ; then
     export PATH="\${GOENV_ROOT}/shims:\${PATH}"
   else
     export PATH="\${PATH}:\${GOENV_ROOT}/shims"