Minor C language style and reliability fixes

[ppentchev]

Hi,

Thanks for working on deltarpm!

What do you think about these mostly trivial changes that were mostly suggested by the cppcheck tool? I recently applied it to the Debian package of deltarpm; you may also view it at https://salsa.debian.org/pkg-rpm-team/deltarpm/-/blob/debian/master/debian/patches/cppcheck.patch

G'luck, Peter