fix the id error in retriangulation

[lpanaf]

A heuristic fix for the id mismatch for the old colmap database. Previously, frame_id / rig_id are randomly assigned when they do not exist in database, now set it to be consistent with the image_id / camera_id.

[Copilot]

Pull request overview

This pull request addresses ID mismatch issues when converting old COLMAP databases to GLOMAP format. The fix ensures that when frame_id or rig_id don't exist in the database, they are assigned values consistent with image_id or camera_id respectively, rather than being randomly incremented.

Changes:

• Modified rig ID assignment logic to use camera_id when no existing rigs are present
• Modified frame ID assignment logic to use image_id when no existing frames are present

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[Copilot]

ID collision bug: When max_rig_id equals 0 but a rig with ID 0 exists in the database, using camera_id directly can cause a collision. For example, if there's an existing rig with ID 0, and a new camera has camera_id=0, this will create a duplicate rig ID. The condition should check whether any rigs exist, not just whether max_rig_id is non-zero. Consider using rigs.empty() or always incrementing from max_rig_id.

Suggested change

	if (max_rig_id != 0)
	// If any rigs already exist, assign a new unique rig ID by incrementing
	// the current maximum. Otherwise, for the very first rig, reuse the
	// camera_id as the rig ID to preserve original behavior.
	if (!rigs.empty())

[Copilot]

ID collision bug: When max_frame_id equals 0 but a frame with ID 0 exists in the database, using image_id directly can cause a collision. For example, if there's an existing frame with ID 0, and an image has image_id=0, this will create a duplicate frame ID. Consider checking frames.empty() or always incrementing from max_frame_id to avoid collisions.