fix(selfhost-lower): null-guard Lcx_SubstEnumName — hStore nodes with null typeName segfaulted buxc2 project (bux_strlen(NULL) via String_Len)

src/hir_lower.bux

@@ -682,6 +682,9 @@ module HirLower {
     }
 
     func Lcx_SubstEnumName(ctx: *LowerCtx, name: String) -> String {
+        // HIR nodes may carry null names (e.g. hStore without typeName);
+        // Nim tolerated nil strings, bux_strlen(NULL) segfaults.
+        if name == null as String { return name; }
         // If name is a bare generic enum name, mangle to concrete name
         var ge: *Decl = Lcx_FindGenericEnum(ctx, name);
         if ge != null as *Decl {