In case you downloaded an update of HeidiSQL this morning, you may have experienced a fatal program crash when starting HeidiSQL. I have just fixed that in r4621, but as your HeidiSQL crashes, you cannot use the auto-updater this time to get rid of that. Instead, please download the build manually from here and place it in the directory where you have installed HeidiSQL.
Sorry to all affected users for the confusion!
And thanks to carella67 and others for reporting that so quickly.