[RF] Renaming dataset fails when total number of dataset in workspace reached 10

[AlkaidCheng]

• Checked for duplicates

Describe the bug

If the number of dataset in a workspace is larger than or equal to 10. Renaming a dataset inside the workspace will not work in the sense that calling ws.data(<new_dataset_name>) will return nil and calling ws.data(<old_dataset_name>) will return the correct dataset but with the name changed.

To Reproduce

import ROOT

ROOT.RooMsgService.instance().getStream(1).removeTopic(ROOT.RooFit.ObjectHandling)

ws = ROOT.RooWorkspace()
ws.factory("Gaussian::pdf(x[0,10],mu[4,0,10],sigma[1.0,0.1,10.0])")
pdf = ws.pdf("pdf")
x = ws.var("x")
n_dataset = 10
for i in range(n_dataset):
	dataset= pdf.generate(ROOT.RooArgSet(x), ROOT.RooFit.NumEvents(1000), ROOT.RooFit.Name(f"asimovData_{i}"))
	ws.Import(dataset)
ws.data("asimovData_0").SetName("combData")
# this gives nil
print(ws.data("combData"))
# this gives "combData"
print(ws.data("asimovData_0").GetName())

If n_dataset is changed to 9, ws.data("combData") will give the correct dataset and ws.data("asimovData_0") will give nil

Setup

ROOT 6.24, 6.26 (from LCG)