Only use matching branch in gzdev if the branch actually exists (#1240)

Signed-off-by: Addisu Z. Taddese <[email protected]>

jenkins-scripts/docker/lib/docker_generate_dockerfile.bash

@@ -58,9 +58,10 @@ ADD https://api.github.com/repos/gazebo-tooling/gzdev/git/refs/heads/$GZDEV_BRAN
 RUN rm -fr ${GZDEV_DIR} \
     && git clone https://github.com/gazebo-tooling/gzdev -b ${GZDEV_BRANCH} ${GZDEV_DIR}
 DELIM_OSRF_REPO_GIT_1
-if [ -n $GZDEV_TRY_BRANCH ]; then
+GZDEV_TRY_BRANCH_URL="https://api.github.com/repos/gazebo-tooling/gzdev/git/refs/heads/$GZDEV_TRY_BRANCH"
+if [ -n $GZDEV_TRY_BRANCH ] && curl --output /dev/null --silent --head --fail $GZDEV_TRY_BRANCH_URL; then
 cat >> Dockerfile << DELIM_OSRF_REPO_GIT_2
-ADD https://api.github.com/repos/gazebo-tooling/gzdev/git/refs/heads/$GZDEV_TRY_BRANCH version.json
+ADD $GZDEV_TRY_BRANCH_URL version.json
 RUN git -C ${GZDEV_DIR} fetch origin $GZDEV_TRY_BRANCH || true;
 RUN git -C ${GZDEV_DIR} checkout $GZDEV_TRY_BRANCH || true;
 DELIM_OSRF_REPO_GIT_2