GlfImage::OpenForReading not guarded against exceptions

[meshula]

GlfImage::OpenForReading attempts to open an image file for reading, and if it's not possible, it returns an empty pointer.

On the other hand, if one of the libraries OIIO uses to open a file throws an exception, it will be unhandled by OIIO, glf, hydra, or usdImagingGL (gazing up the call stack), and throw all the way out to the running application where there's no reasonable way to respond to the exception. Since not loading was already deemed non-fatal by OpenForReading, I think an exception from a loading library should also be treated as non-fatal.

If the call to _OpenForReading were guarded here with a try { } catch(...) { return GlfImageSharedPtr(); } the behavior would be more consistent.

GlfImageSharedPtr
GlfImage::OpenForReading(std::string const & filename, int subimage)
{
    GlfImageRegistry & registry = GlfImageRegistry::GetInstance();

    GlfImageSharedPtr image = registry._ConstructImage(filename);
    if (!image || !image->_OpenForReading(filename, subimage)) {
        return GlfImageSharedPtr();
    }

    return image;
}

[jtran56]

Filed as internal issue #145448.