shill: cellular: Don't crash shill when unable to create cellular adaptor.

This patch doesn't address the root cause of the issue but at least prevents
shill from crashing. We'll need logs to understand why the adaptor is NULL in
this case. Unfortunately, I haven't been able to repro the issue.

BUG=chromium-os:33411
TEST=unit tests

Change-Id: I0c27c337f5ac966e93ee2ea64f952ea32d09df5c
Reviewed-on: https://gerrit.chromium.org/gerrit/30543
Tested-by: Darin Petkov <petkov@chromium.org>
Reviewed-by: Ben Chan <benchan@chromium.org>
Commit-Ready: Darin Petkov <petkov@chromium.org>
diff --git a/cellular_capability_gsm.cc b/cellular_capability_gsm.cc
index a366ec2..4445de9 100644
--- a/cellular_capability_gsm.cc
+++ b/cellular_capability_gsm.cc
@@ -562,8 +562,12 @@
     }
     apn_list_.push_back(props);
   }
-  cellular()->adaptor()->EmitStringmapsChanged(
-      flimflam::kCellularApnListProperty, apn_list_);
+  if (cellular()->adaptor()) {
+    cellular()->adaptor()->EmitStringmapsChanged(
+        flimflam::kCellularApnListProperty, apn_list_);
+  } else {
+    LOG(ERROR) << "Null RPC service adaptor.";
+  }
 }
 
 // always called from an async context