Fix missing initialization of delayChkptEnd

I noticed that in commit 10520f4346876aad4941797c2255a21bdac74739, int delayChkpt has been changed back to bool delayChkpt + bool delayChkptEnd. However,  the initialization to delayChkptEnd is missed in function InitProcess. When autovacuum_proc1 is in RelationTruncate, the delayChkptEnd will be set as true. If autovacuum_proc1 receives a cancel signal and handles it at this time, autovacuum_proc1 will exit without reseting delayChkptEnd in its error handling process. After that, if autovacuum_proc2 reuses this PGPROC structure, the above error will occur.