1. Technical Field The present invention relates to an image forming apparatus and a control method for the same. 2. Related Art Some of conventional image forming apparatuses such as printers are provided with a plurality of paper trays (paper bins). In these image forming apparatuses, paper discharged from an image forming unit is loaded into a specific tray among a plurality of paper bins (hereinafter, “paper load destination setting” for setting a paper load destination). Here, the specific tray is referred to as an “intended load destination tray” and the other trays than the intended load destination tray are referred to as “other than intended load destination trays.” There are also some of the image forming apparatuses having a function of changing an intended load destination tray to another. In this function, the intended load destination tray is changed by one unit of one tray (for example, by four trays) on the condition that a new intended load destination tray is made available by rotating one-pitch trays among the paper bins (in a case of rotating the tray) around a shaft. In some cases, the operator may need to set a paper load destination setting because an image formed by the image forming unit is not printed on the paper that should be discharged. In this case, when the operator tries to change the paper load destination setting, an unintended load destination tray is made available by rotating one-pitch trays by four trays around the shaft, but the new intended load destination tray is not made available. Accordingly, a tray other than the intended load destination tray set by the user is designated as the paper load destination setting. In this case, since the paper load destination setting is not completed, there is a risk that the paper load destination setting cannot be carried out again. Accordingly, there has been proposed a technique for, when a paper load destination setting does not respond to a user operation, rotating all of the paper bins around a shaft by one tray and giving an allowance to a user to make a setting again (see, for example, JP-A-2013-111609). In the technique disclosed in JP-A-2013-111609, when a paper load destination setting does not respond to a user operation, rotating all of the paper bins around the shaft by one tray allows a user to make a setting again. However, depending on the paper type or the like, a paper load destination setting to a certain tray, which is changed by rotating four trays by one pitch around the shaft, becomes not available. For example, it is assumed that an intended load destination tray is a first tray and other than intended load destination trays are second to fifth trays. In this case, when a user rotates first and second trays by one tray and makes a setting on the first tray after loading paper into the first tray, third and fourth trays to be rotated by one pitch around the shaft are third and fifth trays to be made available by rotating four trays by one pitch, and a paper load destination setting to the third tray cannot be made. That is, since the paper load destination setting cannot be made in spite of rotation of four trays, the paper load destination setting is not completed. That is, even in the case where the paper load destination setting is made after rotating all trays around the shaft by one tray, there is a risk that the paper load destination setting cannot be made if the paper load destination setting should be made to a tray other than the intended load destination tray.