TestQuestionPool: Fixed image type detection according to Mantis issue #20395 (resulted in broken imports)

(cherry picked from commit a87074d8)

(cherry picked from commit b982f430)

(cherry picked from commit 28143c28)

(cherry picked from commit c54b0cd2)

(cherry picked from commit 372a8233)

# Conflicts:
#	Services/Mail/classes/class.ilMailFormGUI.php

Workaround for 0018222: XML Parse Error: No memory at line 1, col 20879062 (Code: 1) after LDAP Sync