Don't crash if LANG isn't set

Chrome SSH doesn't set it.

Change-Id: Icc84ff8943a403db4b13f51727c6e83e5ccb5dab
diff --git a/tools/bazel b/tools/bazel
index f6f4c52..25266b8 100755
--- a/tools/bazel
+++ b/tools/bazel
@@ -81,11 +81,14 @@
 ENVIRONMENT_VARIABLES+=(SHELL="${SHELL}")
 ENVIRONMENT_VARIABLES+=(USER="${USER}")
 ENVIRONMENT_VARIABLES+=(PATH="${PATH}")
-ENVIRONMENT_VARIABLES+=(LANG="${LANG}")
 ENVIRONMENT_VARIABLES+=(HOME="${HOME}")
 ENVIRONMENT_VARIABLES+=(LOGNAME="${LOGNAME}")
 ENVIRONMENT_VARIABLES+=(TERM="${TERM}")
 
+if [[ ! -z "${LANG+x}" ]]; then
+  ENVIRONMENT_VARIABLES+=(LANG="${LANG}")
+fi
+
 if [[ ! -z "${DISPLAY+x}" ]]; then
   ENVIRONMENT_VARIABLES+=(DISPLAY="${DISPLAY}")
 fi