Accept PSAM files without FID column

[Eldergenix]

Fixes #666

Summary

• allow .psam headers that start with #IID when #FID is absent
• use an internal FID value of 0 for absent-FID PSAM samples
• apply the same header and ID handling to the primary PGEN reader and external PGEN reader
• keep malformed rows rejected, including rows missing a declared SEX column

Validation

• g++ -std=c++11 -fsyntax-only src/Geno.cpp -I./src -I./external_libs/pgenlib -I./external_libs/pgenlib/simde -I./external_libs/pgenlib/include -I./external_libs/cxxopts/include -I./external_libs/LBFGSpp/include -I./external_libs/eigen-3.4.0 -I./external_libs/remeta -I./external_libs -I/tmp/regenie-bgen-v1.1.7 -I/tmp/regenie-bgen-v1.1.7/genfile/include -I/tmp/regenie-bgen-v1.1.7/3rd_party/boost_1_55_0 -I/tmp/regenie-bgen-v1.1.7/3rd_party/zstd-1.1.0/lib -I/tmp/regenie-bgen-v1.1.7/db/include -I/tmp/regenie-bgen-v1.1.7/3rd_party/sqlite3 - passed; warnings only from existing vendored/old dependency headers
• git diff --check HEAD~1..HEAD - passed

Not run

• Full local build/test suite was not run because cmake and gfortran are not installed in my local environment.
• Docker-based build/test was not run because the Docker daemon is unavailable locally.