Fix VDisk premature donor drop (#15400)

Author: alexvru

ydb/core/blobstorage/vdisk/repl/blobstorage_repl.cpp

@@ -177,6 +177,7 @@ namespace NKikimr {
         bool UnrecoveredNonphantomBlobs = false;
         bool RequestedReplicationToken = false;
         bool HoldingReplicationToken = false;
+        bool CanDropDonor = false;
 
         TWatchdogTimer<TEvReplCheckProgress> ReplProgressWatchdog;
 
@@ -280,6 +281,7 @@ namespace NKikimr {
             // switch to planning state
             Transition(Relaxation, Plan);
 
+            CanDropDonor = true;
             RunRepl(TLogoBlobID());
         }
 
@@ -375,6 +377,8 @@ namespace NKikimr {
                 ResetReplProgressTimer(false);
             }
 
+            CanDropDonor = CanDropDonor && info->DropDonor;
+
             bool finished = false;
 
             if (info->Eof) { // when it is the last quantum for some donor, rotate the blob sets
@@ -399,7 +403,7 @@ namespace NKikimr {
                     }
                 }
                 if (!finished) {
-                    if (info->DropDonor) {
+                    if (CanDropDonor) {
                         Y_ABORT_UNLESS(!DonorQueue.empty() && DonorQueue.front());
                         DropDonor(*DonorQueue.front());
                         DonorQueue.pop_front();