Array out of bounds warnings

[Flowdalic]

Compiling fragview 0.1.2 on Gentoo triggers a few "array out of bounds" warnings:

 * QA Notice: Package triggers severe warnings which indicate that it
 *            may exhibit random runtime failures.
 * /var/tmp/portage/sys-fs/fragview-0.1.2/work/fragview-0.1.2/src/clusters.cc:447:42: warning: array subscript last_entry is outside array bounds of ‘fiemap_extent [0]’ [-Warray-bounds]
 * /var/tmp/portage/sys-fs/fragview-0.1.2/work/fragview-0.1.2/src/clusters.cc:447:86: warning: array subscript last_entry is outside array bounds of ‘fiemap_extent [0]’ [-Warray-bounds]
 * /var/tmp/portage/sys-fs/fragview-0.1.2/work/fragview-0.1.2/src/clusters.cc:432:46: warning: array subscript k is outside array bounds of ‘fiemap_extent [0]’ [-Warray-bounds]
 * /var/tmp/portage/sys-fs/fragview-0.1.2/work/fragview-0.1.2/src/clusters.cc:431:45: warning: array subscript k is outside array bounds of ‘fiemap_extent [0]’ [-Warray-bounds]
 

[i-rinat]

This particular warning is imminent in the long run, as there are actual out of bounds accesses that are required to use the FIEMAP API. It's possible to hide them from compiler, which I did. There were also other warnings that were fixed as well.
I've pushed the updated version of the code and a new tag, v0.1.3.