New repository is not completely loaded when `packages/opam` path exists

[rjbou]

If a new repository (no diff loading) contains the path packages/opam, opam tries to load that opam file, soft fails, doesn't read the other paths under packages/ and register the repository.

opam/tests/reftests/repository-layout.test

Lines 2169 to 2196 in 6c5857a

	### OPAMDEBUGSECTIONS="FILE(opam) opam-file RSTATE UPDATE" OPAMDEBUG=-3 opam repository add new-default-strict ./REPO --this-switch --strict
	FILE(config) Read ${BASEDIR}/OPAM/config in 0.000s
	RSTATE LOAD-REPOSITORY-STATE @ ${BASEDIR}/OPAM
	RSTATE Cache found
	[new-default-strict] Initialised
	UPDATE Repository has new changes
	RSTATE load repo new-default-strict from dir
	FILE(opam) Read packages/opam (out of ${BASEDIR}/OPAM/repo/new-default-strict) in 0.000s
	RSTATE ERR: directory name not a valid package: ignored ${BASEDIR}/OPAM/repo/new-default-strict/packages/opam
	### OPAMDEBUGSECTIONS="FILE(opam) opam-file RSTATE UPDATE" OPAMDEBUG=-3 opam repository add new-default ./REPO --this-switch
	FILE(config) Read ${BASEDIR}/OPAM/config in 0.000s
	RSTATE LOAD-REPOSITORY-STATE @ ${BASEDIR}/OPAM
	RSTATE Cache found
	[new-default] Initialised
	UPDATE Repository has new changes
	RSTATE load repo new-default from dir
	FILE(opam) Read packages/opam (out of ${BASEDIR}/OPAM/repo/new-default) in 0.000s
	RSTATE ERR: directory name not a valid package: ignored ${BASEDIR}/OPAM/repo/new-default/packages/opam
	### :XII:1:b: List available package
	### opam switch create opam-at-root-pkg-sw-from-scratch --empty --repo=new-default,new-default-strict
	### opam repository --this-switch
	<><> Repository configuration for switch opam-at-root-pkg-sw-from-scratch <><><>
	1 new-default file://${BASEDIR}/REPO
	2 new-default-strict file://${BASEDIR}/REPO
	### opam list -A --repo new-default-strict
	# Packages matching: from-repository(new-default-strict) & any
	# No matches found

Found when looking at #6871 & #6924

[kit-ty-kate]

this is also true for any directory under packages/ that contain an invalid opam file or if the directory doesn't have the right <pkgname>.<pkgver> pattern. For example /packages/test/opam or /packages/test/test/opam is also affected

[rjbou]

Opam files that are not under <pkgname>.<pkgver>/opam pattern are intentionally not loaded.
It is true that currently any path that have the pattern packages/[.*]/opam where opam is not an opam file will not read opam files under packages/[.*] directory, even if it is a valid path.
The issue is much more impacting if that non opam file is directly at packages/opam, nothing is loaded: the repository loading succeed, but it is empty.