Fix travis_fastfail.sh for null case

when an old PR build gets restarted after some time, the travis API request
might not return enough builds to include the most recent one for the PR,
so the null result would incorrectly cause a 'superceded' fast-fail condition

contrib/travis_fastfail.sh

@@ -5,9 +5,10 @@ curlhdr="Accept: application/vnd.travis-ci.2+json"
 endpoint="https://api.travis-ci.org/repos/$TRAVIS_REPO_SLUG"
 
 # Fail fast for superseded builds to PR's
-if ! [ "$TRAVIS_PULL_REQUEST" = "false" ]; then
-  if ! [ \"$TRAVIS_BUILD_NUMBER\" = $(curl -H "$curlhdr" $endpoint/builds?event_type=pull_request | \
-      jq ".builds | map(select(.pull_request_number == $TRAVIS_PULL_REQUEST))[0].number") ]; then
+if [ "$TRAVIS_PULL_REQUEST" != "false" ]; then
+  newestbuildforthisPR=$(curl -H "$curlhdr" $endpoint/builds?event_type=pull_request | \
+      jq ".builds | map(select(.pull_request_number == $TRAVIS_PULL_REQUEST))[0].number")
+  if [ $newestbuildforthisPR != null -a $newestbuildforthisPR != \"$TRAVIS_BUILD_NUMBER\" ]; then
     echo "There are newer queued builds for this pull request, failing early."
     exit 1
   fi
@@ -17,7 +18,7 @@ else
     master | release*)
       ;;
     *)
-      if ! [ \"$TRAVIS_BUILD_NUMBER\" = $(curl -H "$curlhdr" \
+      if [ \"$TRAVIS_BUILD_NUMBER\" != $(curl -H "$curlhdr" \
           $endpoint/branches/$TRAVIS_BRANCH | jq ".branch.number") ]; then
         echo "There are newer queued builds for this branch, failing early."
         exit 1