Return error code when get_images_from_skps has failures

tools/get_images_from_skps.cpp

 /*
  * Copyright 2016 Google Inc.
  *
  * Use of this source code is governed by a BSD-style license that can be
  * found in the LICENSE file.
  */
 
 #include "SkBitmap.h"
 #include "SkCodec.h"
 #include "SkCommandLineFlags.h"
@@ skipping 139 matching lines @@
     Json::Value fRoot;
     for(auto it = gSkpToUnknownCount.cbegin(); it != gSkpToUnknownCount.cend(); ++it)
     {
         SkDebugf("%s %d\n", it->first.c_str(), it->second);
         totalUnknowns += it->second;
         fRoot["failures"][it->first.c_str()] = it->second;
     }
     SkDebugf("%d known, %d unknown\n", gKnown, totalUnknowns);
     fRoot["totalFailures"] = totalUnknowns;
     fRoot["totalSuccesses"] = gKnown;
-    if (totalUnknowns > 0 && !FLAGS_failuresJsonPath.isEmpty()) {
-        SkDebugf("Writing failures to %s\n", FLAGS_failuresJsonPath[0]);
-        SkFILEWStream stream(FLAGS_failuresJsonPath[0]);
-        stream.writeText(Json::StyledWriter().write(fRoot).c_str());
-        stream.flush();
+    if (totalUnknowns > 0) {
+        if (!FLAGS_failuresJsonPath.isEmpty()) {
+            SkDebugf("Writing failures to %s\n", FLAGS_failuresJsonPath[0]);
+            SkFILEWStream stream(FLAGS_failuresJsonPath[0]);
+            stream.writeText(Json::StyledWriter().write(fRoot).c_str());
+            stream.flush();
+        }
+        return -1;
     }
-
     return 0;
 }