meta-google: gbmc-bridge: fail upgrade when url is invalid

Currently the upgrade will continue when there is no url. This change
will stop self update if the url is empty/invalid.

Change-Id: I465ee426c845b918aa458b24db89fbcc2795cde5
Signed-off-by: Yuxiao Zhang <yuxiaozhang@google.com>
diff --git a/meta-google/recipes-phosphor/flash/gbmc-update/40-gbmc-upgrade.sh b/meta-google/recipes-phosphor/flash/gbmc-update/40-gbmc-upgrade.sh
index 0b927f0..3ac4020 100644
--- a/meta-google/recipes-phosphor/flash/gbmc-update/40-gbmc-upgrade.sh
+++ b/meta-google/recipes-phosphor/flash/gbmc-update/40-gbmc-upgrade.sh
@@ -78,8 +78,14 @@
 
   local tmpdir
   tmpdir="$(mktemp -d)" || return
+  if ! gbmc_upgrade_dl_unpack; then
+    echo 'upgrade unpack failed' >&2
+    # shellcheck disable=SC2153
+    rm -rf -- "$tmpdir" "$GBMC_UPGRADE_SIG" "$GBMC_UPGRADE_IMG"
+    return 1
+  fi
   # shellcheck disable=SC2015
-  gbmc_upgrade_dl_unpack && gbmc_br_run_hooks GBMC_UPGRADE_HOOKS || true
+  gbmc_br_run_hooks GBMC_UPGRADE_HOOKS || true
   # shellcheck disable=SC2153
   rm -rf -- "$tmpdir" "$GBMC_UPGRADE_SIG" "$GBMC_UPGRADE_IMG"
 }