Fix bug setting COMPOSER_ORIGINAL_INIS
Fix bug setting COMPOSER_ORIGINAL_INIS

This variable stores the loaded ini file and any additional scanned ini
files, separated by a path-separator. The loaded ini file should always
be present, even if it is an empty value. Unfortunately I removed any
empty value to parse the ini files, then used the truncated list to set
the variable.

This bug surfaced on docker php images. These do not have a specific
php.ini but store all their settings in the location(s) configured at
build time using --with-config-file-scan-dir.

stefangr/composer,gencer/composer,milleruk/composer,fabpot/composer,pierredup/composer,alcohol/composer,staabm/composer,nicolas-grekas/composer,erasys/composer,johnstevenson/composer,composer/composer,naderman/composer,floverdevel/composer,dzuelke/composer,stof/composer,vdm-io/composer,slbmeh/composer,andrerom/composer,SpacePossum/composer,localheinz/composer