Don't assume that struct types have at least one field

In some cases that may not be true with the information at hand (e.g.
grididps binary from AMP which had incomplete arduino types).

Author: waskyo

CodeHawk/CHB/bchlib/bCHBCTypeUtil.ml

@@ -949,27 +949,31 @@ let get_compinfo_field (c: bcompinfo_t) (fname: string): bfieldinfo_t =
 let get_struct_field_at_offset
       (cinfo: bcompinfo_t) (offset: int): (bfieldinfo_t * int) option =
   let finfos = cinfo.bcfields in
-  let field0 = List.hd finfos in
-  if offset = 0 then
-    Some (field0, 0)
+  (* Some struct types may be incomplete and not have any fields at all *)
+  if (List.length finfos) = 0 then
+    None
   else
-    let field0type = resolve_type field0.bftype in
-    if offset < size_of_btype field0type then
-      Some (field0, offset)
+    let field0 = List.hd finfos in
+    if offset = 0 then
+      Some (field0, 0)
     else
-      List.fold_left (fun acc finfo ->
-          match acc with
-          | Some _ -> acc
-          | _ ->
-             match finfo.bfieldlayout with
-             | Some (foffset, size) ->
-                if offset = foffset then
-                  Some (finfo, 0)
-                else if offset > foffset && offset < foffset + size then
-                  Some (finfo, offset - foffset)
-                else
-                  None
-             | _ -> None) None finfos
+      let field0type = resolve_type field0.bftype in
+      if offset < size_of_btype field0type then
+        Some (field0, offset)
+      else
+        List.fold_left (fun acc finfo ->
+            match acc with
+            | Some _ -> acc
+            | _ ->
+               match finfo.bfieldlayout with
+               | Some (foffset, size) ->
+                  if offset = foffset then
+                    Some (finfo, 0)
+                  else if offset > foffset && offset < foffset + size then
+                    Some (finfo, offset - foffset)
+                  else
+                    None
+               | _ -> None) None finfos
 
 
 let rec get_compinfo_scalar_type_at_offset