fix: Edge case when paging from a line within prompt

When PROMPT_START is already past scrollback and can't be
found upwards, set the proper values depending on if the
search is over or deferred downwards.

kitty/screen.c

@@ -4122,7 +4122,8 @@ find_cmd_output(Screen *self, OutputOffset *oo, index_type start_screen_y, unsig
         }
         if (y1 < upward_limit) {
             oo->reached_upper_limit = true;
-            found_output = true; start = upward_limit;
+            found_output = direction != 0; start = upward_limit;
+            found_prompt = direction != 0;
         }
     }