Integer types in header data should be interpreted as unsigned

[aft90]

Sorry if the title isn't clear, but basically when an index record says that its data is of type, say, RPM_INT16_TYPE, the corresponding data should be interpreted as an unsigned integer, whereas currently the implementation interprets it as signed.

Here is a reference to the RPM docs saying so: https://github.com/rpm-software-management/rpm/blob/master/docs/manual/tags.md#scalar-types

There are four unsigned integer types for RPM tags:

Additionally, if you look in the rpm C code, you can see there are a lot of references to headers using unsigned int values for data, and none using signed ints - for instance here: https://github.com/rpm-software-management/rpm/blob/master/include/rpm/header.h#L205

Anecdotally, I first realised this was an issue when I was using your library to test some RPMs I'm building with an automated tool. I wanted to verify the permissions on the files were being set right so I retrieved headers['filemodes'][x] and tried to use the stat functions on the value (the RPM spec says that filemodes should be identical to st_mode in struct stat). However I kept getting OverflowError: can't convert negative value to unsigned int which made me wonder if the values ought to be unsigned.

If I understand the issue correctly, it should be a small change to extract_int16 and extract_int32. I'll raise a PR shortly.

hello-2.12.1-2.fc39.x86_64.rpm.gz