HPCC-17702 Fix migratefiles mid-group offset issue.

If a file had been created on a subset of a group's nodes,
e.g. thor400_30[16-17] - the target group name was incorrectly
offset by -1.

Signed-off-by: Jake Smith <jake.smith@lexisnexisrisk.com>

dali/daliadmin/daliadmin.cpp

@@ -2985,7 +2985,7 @@ static void migrateFiles(const char *srcGroup, const char *tgtGroup, const char
                                 if (NotFound == groupOffset)
                                     groupOffset = srcRelPos;
                                 unsigned dstRelPos = srcRelPos % tgtClusterSize;
-                                dstPositions.append(dstRelPos);
+                                dstPositions.append(dstRelPos+1);
                             }
                             StringBuffer rangeText;
                             encodeChildGroupRange(dstPositions, rangeText);