qmemman: add some comments about new condition for failing request
qmemman: add some comments about new condition for failing request

QubesOS/qubes-issues#1136

woju/qubes-core-admin,marmarek/qubes-core-admin,QubesOS/qubes-core-admin,woju/qubes-core-admin,QubesOS/qubes-core-admin,marmarek/qubes-core-admin,QubesOS/qubes-core-admin,woju/qubes-core-admin,marmarek/qubes-core-admin,woju/qubes-core-admin