loader: make sure we always return an error even without type errors

This issue was originally reported here:
https://github.com/NixOS/nixpkgs/pull/341170#issuecomment-2359237471

The fix here isn't a great fix, it turns the error message from this:

    # runtime/interrupt

into this:

    # runtime/interrupt
    package requires newer Go version go1.23

...so not great, because it doesn't show the real error message (which
is that TinyGo wasn't compiled with the right Go version). But at least
it gives a hint in the right direction.

It's difficult to test for this specific case, so I've left out testing
in this case (boo!)

loader/loader.go

@@ -432,7 +432,15 @@ func (p *Package) Check() error {
 		if err, ok := err.(Errors); ok {
 			return err
 		}
-		return Errors{p, typeErrors}
+		if len(typeErrors) != 0 {
+			// Got type errors, so return them.
+			return Errors{p, typeErrors}
+		}
+		// This can happen in some weird cases.
+		// The only case I know is when compiling a Go 1.23 program, with a
+		// TinyGo version that supports Go 1.23 but is compiled using Go 1.22.
+		// So this should be pretty rare.
+		return Errors{p, []error{err}}
 	}
 	p.Pkg = typesPkg