Adding a check for nullptr in UpdateRecommendedPrinters

R=skau@chromium.org

Bug: 779256
Change-Id: I5772282ee310a594b5e31d5931fa38a6fa67cde8
Reviewed-on: https://chromium-review.googlesource.com/755417Reviewed-by: Sean Kau <skau@chromium.org>
Commit-Queue: David Valleau <valleau@chromium.org>
Cr-Commit-Position: refs/heads/master@{#515980}

chrome/browser/chromeos/printing/synced_printers_manager.cc

@@ -198,9 +198,15 @@ class SyncedPrintersManagerImpl : public SyncedPrintersManager,
         LOG(WARNING) << "Duplicate printer ignored.";
         continue;
       }
+
+      auto new_printer = RecommendedPrinterToPrinter(*printer_dictionary);
+      if (!new_printer) {
+        LOG(WARNING) << "Recommended printer is malformed.";
+        continue;
+      }
+
       new_ids.push_back(id);
-      new_printers.insert(
-          {id, *RecommendedPrinterToPrinter(*printer_dictionary)});
+      new_printers.insert({id, *new_printer});
     }
 
     // Objects not in the most recent update get deallocated after method