Was the stove in use yesterday?
If the glass is fitted tightly and the stove heats up, then cools the constraints on the glass miht cause it to crack.
Or maybe a log or lump of coal tumbled in the fite and knocked the glass, causing it to crack.
Is it safe to light?
General advice is not to light a stove with cracked glass.
1. the glass is weakened and further stress due to heat might lead to complete failure - the glass smashing and exposing the naked fire to the room.
2. a crack will modify the airflow, causing the fire to (probably) burn significantly hotter.
3. before the fire is properly alight, there may be some leakage of carbon monoxide, though if you have a good draw, that's not a huge risk.
My advice:
1. don't burn the stove with cracked glass.
2. Order a replacement immediately
3. If you absolutely must] run the stove, the do not leave it unattended.