Android: fixes bb_device_status_check.

Following crrev.com/213194, imei can be absent on some devices.

BUG=254014
NOTRY=True
TBR=tomhudson@google.com

Review URL: https://codereview.chromium.org/20053005

git-svn-id: http://src.chromium.org/svn/trunk/src/build@213402 4ff67af0-8c30-449e-8e8b-ad334ec8d88c

android/buildbot/bb_device_status_check.py

@@ -59,7 +59,9 @@ def DeviceInfo(serial, options):
     battery_level = int(re.findall('level: (\d+)', battery)[0])
     battery_temp = float(re.findall('temperature: (\d+)', battery)[0]) / 10
   sub_info = device_adb.GetSubscriberInfo()
-  imei_slice = re.findall('Device ID = (\d+)', sub_info)[0][-6:]
+  imei_slice = ''
+  if sub_info and len(sub_info):
+    imei_slice = re.findall('Device ID = (\d+)', sub_info)[0][-6:]
   report = ['Device %s (%s)' % (serial, device_type),
             '  Build: %s (%s)' %
               (device_build, device_adb.GetBuildFingerprint()),