ktxTexture2_GetImageOffset: identifier not found

[UX3D-haertl]

I'm getting this build error, while trying to use ktxTexture2_GetImageOffset (even though my IDE can find the function in the source code).

I'm now using ktxTexture_GetImageOffset(ktxTexture(texture), 0, 0, 0, &offset); instead.

Other texture2 functions such as ktxTexture2_Destroy can be used without problems.

[MarkCallow]

It is not exposed in ktx.h, and therefore on Windows is not added to dll exports (when building libktx) and imports (when compiling apps.)

I'll happily accept a PR to add it to ktx.h.