Add field_resize_raw_if_necessary

field.c

@@ -24,6 +24,12 @@ void field_resize_raw(Field* f, Usz height, Usz width) {
   f->width = (U16)width;
 }
 
+void field_resize_raw_if_necessary(Field* field, Usz height, Usz width) {
+  if (field->height != height || field->width != width) {
+    field_resize_raw(field, height, width);
+  }
+}
+
 void field_deinit(Field* f) { free(f->buffer); }
 
 void field_copy_subrect(Field* src, Field* dest, Usz src_y, Usz src_x,

field.h

@@ -4,6 +4,7 @@
 void field_init(Field* field);
 void field_init_fill(Field* field, Usz height, Usz width, Glyph fill_char);
 void field_resize_raw(Field* field, Usz height, Usz width);
+void field_resize_raw_if_necessary(Field* field, Usz height, Usz width);
 void field_deinit(Field* field);
 void field_copy_subrect(Field* src, Field* dest, Usz src_y, Usz src_x,
                         Usz dest_y, Usz dest_x, Usz height, Usz width);

tui_main.c

@@ -245,6 +245,8 @@ void undo_history_push(Undo_history* hist, Field* field, Usz tick_num) {
       hist->first = new_node->next;
       hist->first->prev = NULL;
     }
+    field_resize_raw_if_necessary(&new_node->field, field->height,
+                                  field->width);
   } else {
     new_node = malloc(sizeof(Undo_node));
     ++hist->count;