Properly set and read is_ref in delegate.hpp to fix non-$this variable source components in query iteration

[Gaspard--]

• set is_ref in populate_self so that it's properly set for any type of query
• always set row to 0 for components with is_ref to avoid indexing garbage

Fixes #1324

[SanderMertens]

Nice! Can you:

• Add a test case that reproduces the bug
• Run bake once on the repository so the distr/flecs.h files get updated? (this is what's causing CI to fail)

[Gaspard--]

I tried to cover some range of scenarios in the test. Didn't add optional arguments because I felt like the test was getting a bit long.

[SanderMertens]

Thanks, almost there:

• Can you split up the test into three individual test cases?
• You'll need to add the test cases to the test/cpp/project.json file for them to be executed

[Gaspard--]

I thought about is some more and I'm pretty sure these 2 tests cover all cases. I wanted to make sure reading / writing relationships was consistent originally, but I'm pretty sure that superfluous.

[SanderMertens]

Thanks for the PR!