Except as provided in subsection (b) of this section, the Board may not issue a license for an establishment that is within 300 feet of a place of worship or a public or nonpublic kindergarten, elementary, or secondary school. The distance from the establishment to the place of worship or the public or nonpublic kindergarten, elementary, or secondary school is to be measured from the nearest wall of the establishment in a direct line to the nearest point of the main building of the place of worship or the school. The prohibition against issuing a license in subsection (a) of this section does not apply: in Leonardtown; or if a place of worship or school locates its building within 300 feet of a premises that is already licensed.