ci.jpl: filterFailedBuild: Don't fail if FAILURE_TESTS: not found

Signed-off-by: Paul Sokolovsky <paul.sokolovsky@linaro.org>
Change-Id: I1a09357ffa18cb0bf8490dcad8935c9c3a1d3472
diff --git a/jenkins/ci.jpl b/jenkins/ci.jpl
index a0bb26e..86e9443 100644
--- a/jenkins/ci.jpl
+++ b/jenkins/ci.jpl
@@ -329,6 +329,9 @@
 def filterFailedTest(string) {
   def failed_tests = [:]
   line = lineInString(string, "FAILURE_TESTS:")
+  if (line == null) {
+    return ["???"];
+  }
   a = line.split(' ')
   if (a.size() > 1) {
     a = line.split(' ')[1..-1]