Fixed 'Optional Texture Embedding' feature

[lufriem]

Description

It seems that commit 68edd8f broke the 'Optional texture embedding' (see PR #172) feature, so that vsgb/vsgt files created using vsgconv will (at best) not work and (at worst) lead to the loading code to crash.

For example it happened to me that I had a top-level CullNode.. the vsg::External object referenced an external texture, but its path was not set/saved (that is the actual bug introduced in the merge), so the StartID_EndID_Filename values were incorrect (an empty object with the ID=3 was created on loading), which means the the vsg::MatrixTransform node was not loaded (since the empty object with ID=3 already cached), so I ended up with a CullNode without child node, which leads to an access violation on traversal (CullNode on purpose does not check for this due to performance considerations)

#vsga 1.1.7
Root id=1 vsg::CullNode
{
userObjects 1
key "external"
object id=2 vsg::External
{
userObjects 0
options id=0
NumEntries 1
StartID_EndID_Filename 3 3 ""
}
bound 2.28881835938e-05 2.22340196371 45.2545385361 63.7056769332
child id=3 vsg::MatrixTransform
{

For reference, after the fix, the file looks like this

#vsga 1.1.7
Root id=1 vsg::CullNode
{
userObjects 1
key "external"
object id=2 vsg::External
{
userObjects 0
options id=0
NumEntries 1
StartID_EndID_Filename 3 4 "myTexture.bmp"
}
bound 2.28881835938e-05 2.22340196371 45.2545385361 63.7056769332
child id=4 vsg::MatrixTransform
{

Fixes #195

Type of change

Please delete options that are not relevant.

• Bug fix (non-breaking change which fixes an issue)

How Has This Been Tested?

I converted some test models using vsgconvd.exe, using the command line

• '--external_textures true --external_texture_format vsgb' and
• '--external_textures true --external_texture_format native'

then loaded the resulting files into the vsgViewer example

Test Configuration:
Windows 10, VS2022

Checklist:

• My code follows the style guidelines of this project
• I have performed a self-review of my own code
• I have commented my code, particularly in hard-to-understand areas
• I have made corresponding changes to the documentation
• My changes generate no new warnings
• I have added tests that prove my fix is effective or that my feature works
• New and existing unit tests pass locally with my changes
• Any dependent changes have been merged and published in downstream modules