add check if exam is visible (#1820)
add check if exam is visible (#1820)

Co-authored-by: Francisco De las Casas Young <c69e55af28401f6403c20bf1fcc5de732aa7c6b2@tum.de>
ls1intum/ArTEMiS,ls1intum/ArTEMiS,ls1intum/ArTEMiS,ls1intum/ArTEMiS,ls1intum/ArTEMiS,ls1intum/ArTEMiS