Fix Command#report_warnings to gracefully handle missing Compiler#program

[straight-shoota]

If the compiler was not setup correctly and program is missing, there are no warnings to show and the method should just return gracefully instead of causing a NilAssertion error.

/cc #9789 (comment)

[bcardiff]

I think it would be more correct to show a STDERR at least.

If the report_warnings is called and the compiler.program is not setup with the proposed change it is harder to notice it.

I'm not even sure this change at all is needed. It's a nilable property that we expect to be set when reporting warnings. If it's not set there is somethings else wrong, better crash or signal the error somehow.

[straight-shoota]

If it's not set there is somethings else wrong, better crash or signal the error somehow.

Exactly that's the case. This change (or something alike) is necessary to make the original error show up. Currently it's shadowed by the NilAssertion error. See #9789 (comment) for details.

IMO this change is fine as it is. This condition only occures when there's already some error handling happening. Notifying about program being nil is completely unnecessary at this point because it's just a secondary error.
Two lines above is an return if @compiler has no value. So calling report_warnings doesn't require a compiler to be set up.

[bcardiff]

ok, thanks for clarifying.