lvm-dbus: Fix calling lvcreate with empty list of PVs

[vojtechtrefny]

GLib really dislikes us calling 'g_variant_builder_end' on the empty array in this case.

Backport of #1125

[gemini-code-assist]

Summary of Changes

Hello @vojtechtrefny, I'm Gemini Code Assist¹! I'm currently reviewing this pull request and will post my feedback shortly. In the meantime, here's a summary to help you and other reviewers quickly get up to speed!

This pull request resolves a bug in the lvm-dbus plugin that occurred when attempting to create a logical volume (lvcreate) without specifying any physical volumes. Previously, this scenario could lead to an incorrect call to g_variant_builder_end with an empty array, causing GLib to misbehave. The change introduces a defensive check to prevent this, ensuring the GVariantBuilder is only initialized when a non-empty list of PVs is provided. A corresponding test case has also been added to validate this fix.

Highlights

• Bug Fix for lvcreate with empty PV list: Corrected an issue in the bd_lvm_lvcreate function where calling g_variant_builder_end with an empty array of Physical Volumes (PVs) could cause problems with GLib.
• Robust Empty List Handling: Added a check for *pv_list to ensure the PV list is not empty before attempting to initialize the GVariantBuilder and iterate through PVs, preventing the problematic GLib call.
• New Test Case: Introduced a new test in tests/lvm_dbus_tests.py to specifically cover the scenario of calling lvm_lvcreate with an empty list of PVs, ensuring the fix works as expected and prevents regressions.

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[gemini-code-assist]

Code Review

This pull request correctly fixes a bug in bd_lvm_lvcreate that could lead to a crash when an empty list of PVs was provided. The change to the conditional check ensures that empty lists are handled properly, preventing an issue with g_variant_builder_end. The addition of a new test case in tests/lvm_dbus_tests.py is excellent, as it specifically covers this scenario and prevents future regressions. The changes are concise, correct, and well-tested.