In your case, the company can hold its Annual General Meeting (AGM) without holding an EGM to appoint a new auditor as the Board of Directors has already filled the casual vacancy of the auditor on 20th April 2018.
Just telling, had the board of directors not filled the casual vacancy in the auditors' office before the company's AGM, then the company must hold an EGM before the AGM for filling the casual vacancy of the auditor.
FYI, as per the Companies Act, 2013, a company can fill a casual vacancy in the office in an extraordinary general meeting (EGM) of the company.
This is because the appointment of an auditor is an important matter and it is mandatory to have an auditor in place before the AGM.