openSUSE 15.4 / g++ v7.5.0 build warnings

[d99kris]

Description:
Building rapidcsv on openSUSE 15.4 / g++ v7.5.0 generates warnings like the following:

In file included from /root/rapidcsv/tests/ptest001.cpp:3:0:

/root/rapidcsv/src/rapidcsv.h: In member function ‘size_t rapidcsv::Document::GetDataRowIndex(size_t) const’:
/root/rapidcsv/src/rapidcsv.h:1764:24: warning: conversion to ‘long unsigned int’ from ‘int’ may change the sign of the result
[-Wsign-conversion]
       return pRowIdx + static_cast<size_t>(mLabelParams.mColumnNameIdx + 1);
                        ^~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~

/root/rapidcsv/src/rapidcsv.h: In member function ‘size_t rapidcsv::Document::GetDataColumnIndex(size_t) const’:
/root/rapidcsv/src/rapidcsv.h:1769:27: warning: conversion to ‘long unsigned int’ from ‘int’ may change the sign of the result
[-Wsign-conversion]
       return pColumnIdx + static_cast<size_t>(mLabelParams.mRowNameIdx + 1);
                           ^~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~

While harmless in practise, it would be good to build without warnings.

Thanks to Randall for reporting this issue via email.

How to reproduce it:

zypper install git cmake gcc gcc-c++
git clone https://github.com/d99kris/rapidcsv && cd rapidcsv
./make.sh build

Environment:

• Version: v8.77
• OS / distro: openSUSE 15.4