[ActivityManager] Ensure provider external access count will be released.

Sympton: Oom-adj of provider process will be always 0.

Root Cause: Exception happend in openContentUri
may not call removeContentProviderExternalUnchecked.

Flow:
application [MediaPlayer.setDataSource(Context context, Uri uri)]
    uri is invalid, IOException will be caught and below log will appear:
    "Couldn't open file on client side, trying server side"
    Continue to call setDataSource(String path, Map<String, String> headers)
 ->mediaserver [MediaPlayerService::Client::setDataSource]
    setDataSource(httpService, url, headers) calls openContentProviderFile
 ->system_server (ActivityManagerService) [openContentUri]
    Increase externalProcessNoHandleCount for media provider.
    Call [openFile] to media provider.
 ->android.process.media [check permission for openFile]
    enforceReadPermissionInner
 ->system_server [checkComponentPermission]
    Use mediaserver's uid to check READ_EXTERNAL_STORAGE
      -> not granted due to it is pure native process, not a known package.
    Throw security exception then the flow of openContentUri is broke.
    And externalProcessNoHandleCount is unable to decrease.

Application sample code:
 String invalidId = "54321";
 Uri externalUri = MediaStore.Files.getContentUri("external");
 Uri uri = Uri.withAppendedPath(externalUri, invalidId);
 mediaPlayer.setDataSource(mContext, uri);

Solution: Move removeContentProviderExternalUnchecked to finally block.

Change-Id: I75eec1f9631e9c6bb18449946d707d51ac21e8a7