remote_gcc_build: fix branch setting error.

This fixes the error when a version is given, the branch
it empty, it invokes the cbuildbot in a wrong way.

BUG=None
TEST=./remote_gcc_build.py -t lumpy-release -c ~/clang -p 51046
     -d ~/local_tmp -r --chromeos_version R29-4165.0.0 passes.

Change-Id: I75e24dc1c820583ecb0a10183d9bc86bdec50fbb
Reviewed-on: https://gerrit-int.chromium.org/38595
Commit-Queue: Yunlian Jiang <yunlian@google.com>
Reviewed-by: Yunlian Jiang <yunlian@google.com>
Tested-by: Yunlian Jiang <yunlian@google.com>
1 file changed