SEOUL (Reuters) – Samsung Electronics Co Ltd estimated its October-December operating profit fell 18 percent to 8.3 trillion won ($7.8 billion) from the prior quarters record earnings due to a one-off special bonus and heightened competition with Apple Inc. The guidance, released on Tuesday ahead of full quarterly results scheduled for January 24, was lower than a 9.75 trillion won Thomson Reuters Starmine SmartEstimate of 23 analysts, which gives greater weighting to the more accurate analysts. The South Korean company estimated fourth-quarter sales of 59. …