Attach source edges to :uninferred generator CodeInstance (#58324)

I am not sure when we may be in the situation where `edges` is `null`,
but if we do, we crash.

I triggered such a crash in
JuliaComputing/DAECompiler.jl#24, which manually adds
edges to handcrafted code instances. I may be doing something wrong, but
in any case, it doesn't hurt to be more robust (and perhaps handle this
situation more gracefully).

---------

Co-authored-by: Jameson Nash <[email protected]>

Author: serenity4

src/toplevel.c

@@ -517,11 +517,15 @@ int jl_needs_lowering(jl_value_t *e) JL_NOTSAFEPOINT
 
 JL_DLLEXPORT jl_code_instance_t *jl_new_codeinst_for_uninferred(jl_method_instance_t *mi, jl_code_info_t *src)
 {
+    jl_svec_t *edges = jl_emptysvec;
+    if (src->edges && jl_is_svec(src->edges))
+        edges = (jl_svec_t*)src->edges;
+
     // Do not compress this, we expect it to be shortlived.
     jl_code_instance_t *ci = jl_new_codeinst(mi, (jl_value_t*)jl_uninferred_sym,
         (jl_value_t*)jl_any_type, (jl_value_t*)jl_any_type, jl_nothing,
         (jl_value_t*)src, 0, src->min_world, src->max_world,
-        0, NULL, NULL, NULL);
+        0, NULL, NULL, edges);
     return ci;
 }