return umf_result in (almost) all umf functions

[lplewa]

Description

Checklist

• Code compiles without errors locally
• All tests pass locally
• CI workflows execute properly

• CI workflows, not executed per PR (e.g. Nightly), execute properly
• New tests added, especially if they will fail without my changes
• Added/extended example(s) to cover this functionality
• Extended the README/documentation
• All newly added source files have a license
• All newly added source files are referenced in CMake files
• Logger (with debug/info/... messages) is used
• All API changes are reflected in docs and def/map files, and are tested

[KFilipek]

Suggested change

	*name = "File Provider";
	if(name == NULL) {
	return NULL;
	}
	*name = "File Provider";

[KFilipek]

or ASSERT

[lplewa]

done

[bratpiorka]

@lplewa - about compatibility - please disable these tests in separate commit, then we merge this PR, create new tag and update compatibility workflow + enable it