URDF import fails if collision STL mesh files have same names as visual STL mesh files

[KeiranCantilina]

Describe the bug
URDF-importer tries to find the collision prefabs it created in the visual mesh folder if the visual and collision STL files have the same name. Conversely, it then uses the collision meshes for the visual mesh instead. This problem doesn't occur if the STL files for the collision meshes have different names than the visual mesh STL files.

To Reproduce
Steps to reproduce the behavior:

1. Name visual STLs identically to the corresponding collision STLs
2. Generate urdf from xacro.urdf.
3. Try to import URDF in Unity using importer

Environment (please complete the following information, where applicable):

• Unity Version: Unity 2022.3.1f1
• Unity machine OS + version: Windows 10
• ROS machine OS + version: ROS melodic-robot Docker image
• ROS–Unity communication: Docker
• Branch or version: v0.5.2