Handle jagged leaf-list

[jpivarski]

Sometimes, ROOT produces TBranches with types like

leaf1[counter]/F:leaf2[counter]/I:leaf3[counter]/F

That is, there are multiple TLeaves, the data are interleaved, but the number of items per entry is variable and determined by some other TBranch/TLeaf named counter. This is only conceivably possible if all of the TLeaves in the leaf-list have the same counter, but presumably ROOT ensures that this is the case.

We just need an example file...

[jpivarski]

Cc @mohankarthikg, if you can post a small (< 3 MB), non-private file here, we can add it to our testing suite and ensure that this case will always work in the future. Thanks!