Fixes a file descriptor leak when determining build type

assets/cast_config was being accessed.

Bug: Internal 111712809
Test: Verified that file descriptors were no longer being leaked when
Change-Id: Ide58d71f9f284255cb1d73f3dadae111875be453
Reviewed-on: https://chromium-review.googlesource.com/1148686Reviewed-by: Luke Halliwell <halliwell@chromium.org>
Commit-Queue: Jeremy Newton-Smith <jeremyns@chromium.org>
Cr-Commit-Position: refs/heads/master@{#577651}

chromecast/base/cast_sys_info_android.cc

@@ -40,6 +40,8 @@ bool DoesCastConfigFileExist() {
   base::MemoryMappedFile::Region config_region;
   int config_fd =
       base::android::OpenApkAsset(kCastConfigAssetPath, &config_region);
+  if (config_fd > 0)
+    close(config_fd);
   return config_fd > 0;
 }
 }  // namespace