BUG#20823 testBackup FailMaster failing

  
few cases not handled properly (NF occurs).

ndb/src/kernel/blocks/backup/Backup.cpp

@@ -274,8 +274,18 @@ Backup::execCONTINUEB(Signal* signal)
 
     BackupRecordPtr ptr;
     c_backupPool.getPtr(ptr, ptr_I);
+
+    if (tabPtr_I == RNIL)
+    {
+      closeFiles(signal, ptr);
+      return;
+    }
+    jam();
     TablePtr tabPtr;
     ptr.p->tables.getPtr(tabPtr, tabPtr_I);
+    jam();
+    if(tabPtr.p->fragments.getSize())
+    {
       FragmentPtr fragPtr;
       tabPtr.p->fragments.getPtr(fragPtr, fragPtr_I);
 
@@ -304,6 +314,8 @@ Backup::execCONTINUEB(Signal* signal)
       filePtr.p->operation.dataBuffer.updateWritePtr(sz);
 
       fragPtr_I++;
+    }
+
     if (fragPtr_I == tabPtr.p->fragments.getSize())
     {
       signal->theData[0] = tabPtr.p->tableId;
@@ -4243,6 +4255,12 @@ Backup::execSTOP_BACKUP_REQ(Signal* signal)
       TablePtr tabPtr;
       ptr.p->tables.first(tabPtr);
 
+      if (tabPtr.i == RNIL)
+      {
+        closeFiles(signal, ptr);
+        return;
+      }
+
       signal->theData[0] = BackupContinueB::BACKUP_FRAGMENT_INFO;
       signal->theData[1] = ptr.i;
       signal->theData[2] = tabPtr.i;