Handle headers for integer types with precision cascades

[genevb]

Blast does not provide the precision cascade functionality to integer-types, and they are appropriately differentiated from real-type data in core/accelogic/src/ZipAccelogic.cxx. In principle, the cascade settings should be irrelevant for such types, but the tasks for setting up a precision cascade are done without any check on the data type, so the TBranchPrecisionCascade objects and cascade files are all done before ZipAccelogic's functionality is called. It is simpler to make sure those objects are properly handled for this case than it is to put in the logic to avoid setting up the TBranchPrecisionCascade objects for integer types, even though the latter might seem "cleaner" from a user perspective.

To that end, even if a TBranchPrecisionCascade is generated for such types, the information in the auxiliary cascade tiers should be unimportant. But headers are necessary for these objects to make sense, and presently there is an attempt to read the headers but they don't make sense. This commit achieves the desired result, with appropriate headers indicating that there is no actual content in the auxiliary tiers.

I have done some testing, including reading back with and without the auxiliary files demonstrating that they are in fact inconsequential for the readback.

[pcanal]

thanks.