nulldref possible on Switch block

[seang-ilm]

A tidied up fuzz finding. This one's on a highly infeasible path.

You'll only see it triggered if you have MATERIALX_DYNAMIC_ANALYSIS=ON.

If you add this test case to MaterialXTest/MaterialXCore/Document.cpp

TEST_CASE("Document upgrade switch null value", "[document]")
{
    mx::DocumentPtr doc = mx::createDocument();
    mx::XmlReadOptions readOptions;
    readOptions.upgradeVersion = false;
    mx::readFromXmlString(
        doc,
        R"(<?xml version="1.0"?>
            <materialx version="1.38">
            <nodegraph name="NG1">
                <switch name="sw1" type="integer" nodedef="ND_switch">
                    <input name="which" type="integer" value="abc"/>
                </switch>
            </nodegraph>
            </materialx>
            )",
        mx::FileSearchPath(),
        &readOptions
    );
    REQUIRE_NOTHROW(doc->upgradeVersion());
}

/home/sean/MaterialX/source/MaterialXCore/Version.cpp:1171:45: runtime error: member call on null pointer of type 'struct element_type'

It looks like it's specifically in the upgrade path for 1.38-1.39. When which can't be parsed it returns null.

I think it just needs a null check before accessing it in this block.

void Document::upgradeVersion()
...

    // Upgrade from 1.38 to 1.39
    if (majorVersion == 1 && minorVersion == 38)

            else if (nodeCategory == "switch")
            {
                // Upgrade switch nodes from 5 to 10 inputs, handling the fallback behavior for
                // constant "which" values that were previously out of range.
                InputPtr which = node->getInput("which");
                if (which && which->hasValue())
                {
                    auto whichValue = which->getValue(); // <-- returns null
                    if (whichValue->isA<int>() && whichValue->asA<int>() >= 5) // <-- nulldref here

MaterialX/source/MaterialXCore/Version.cpp

Lines 1190 to 1207 in 8b4b222

	else if (nodeCategory == "switch")
	{
	// Upgrade switch nodes from 5 to 10 inputs, handling the fallback behavior for
	// constant "which" values that were previously out of range.
	InputPtr which = node->getInput("which");
	if (which && which->hasValue())
	{
	auto whichValue = which->getValue();
	if (whichValue->isA<int>() && whichValue->asA<int>() >= 5)
	{
	which->setValue(0);
	}
	else if (whichValue->isA<float>() && whichValue->asA<float>() >= 5)
	{
	which->setValue(0.0);
	}
	}
	}

[kshivam4781]

Opened a PR for this: #3069