When searching for a file extension, it's generally preferable to begin
the search at the end of the string rather than the beginning, as the
whole string isn't going to be walked just to check for something at the
end of it.
If an error occurs when constructing the PartitionFilesystem instance,
the constructor would be exited early, which wouldn't initialize the
extracted data member, making it possible for other code to perform an
uninitialized read by calling the public IsExtractedType() member
function. This prevents that.
Like the other two bits of factored out code, this can also be put
within its own function. We can also modify the code so that it accepts
a const reference to a std::vector of files, this way, we can
deduplicate the file retrieval.
Now the constructor for NSP isn't a combination of multiple behaviors in
one spot. It's nice and separate.
This too, is completely separate behavior from what is in the
constructor, so we can move this to its own isolated function to keep
everything self-contained.
