Throw DomException for DOM out-of-memory error conditions

[nikic]

A number of error conditions in DOM can only occur if libxml2 runs out of memory, at least as far as I can see. In such cases we currently do a silent "return false", which violates the DOM spec, and which code is very unlikely to handle sensibly.

Switch these to throw a DomException with INVALID_STATE_ERR type. This error type is chosen because we use for similar checks elsewhere, for example:

php-src/ext/dom/documentfragment.c

Lines 45 to 48 in a733b1a

	if (!nodep) {
	php_dom_throw_error(INVALID_STATE_ERR, 1);
	RETURN_THROWS();
	}

This changes some of the more obvious cases I spotted, but there are probably more.

cc @kocsismate @beberlei

[nikic]

I've pivoted this to throw a custom DomException instead of a fatal error. I think doing that should be uncontroversial...

[nikic]

Okay, I ended up switching this to use INVALID_STATE_ERR instead, after I realized that we already have quite a few checks like these and they seem to pretty consistently use INVALID_STATE_ERR, so just stick with that. For example:

php-src/ext/dom/documentfragment.c

Lines 45 to 48 in a733b1a

	if (!nodep) {
	php_dom_throw_error(INVALID_STATE_ERR, 1);
	RETURN_THROWS();
	}