struct AD should be deep copied

[Erik Hovland <erik@…>]

In UDFMapICB the code makes a copy of a struct by doing a

      *File = tmpmap.file;

And again:

tmpmap.file = *File;

C++ compilers will likely do the right thing. And even GNU gcc might do the right thing. But it is also possible that the copy won't happen right. In this case, if it got it wrong, then the Partition member of the struct could never get modified throughout the function and then it will be taken as fact that it was and used by this functions callers.

[Erik Hovland <erik@…>]

Does a deep copy of AD structs in UDFMapICB(), note - it is likely that a memcpy could be done too. I didn't to highlight my point. But it may be more efficient.

[danielk]

(In [17208]) Fixes #4841. This one is pretty trivial; some C compilers don't support structure assignment, but all modern ANSI C compilers do; this avoids the structure copy just to be extra safe.