tamer: tameld: Produce first error

...this has apparently been consuming errors for some time.  This would
cause the parser to enter an invalid state in some cases and terminate.

This would _not_ permit an invalid link, as the graph would not be correct,
but it was masking the actual error.

This part of linker is in dire need of tests.  This also ought to be
replaced with tamec's approach of reporting all errors.

DEV-13162

tamer/src/ld/poc.rs

@@ -136,10 +136,11 @@ fn load_xmlo<P: AsRef<Path>, S: Escaper>(
                                 air,
                                 asg,
                                 |end| {
-                                    end.fold(
-                                        Result::<(), TameldError>::Ok(()),
-                                        |x, _| x,
-                                    )
+                                    for result in end {
+                                        let _ = result?;
+                                    }
+
+                                    Ok::<_, TameldError>(())
                                 },
                             )?;