LibIMAP: Make Section::parts unsigned

Author: https://github.com/Lubrsi
Commit: 2c793d5935
Pull-request: https://github.com/SerenityOS/serenity/pull/8826
Reviewed-by: https://github.com/MaxWipfli
Reviewed-by: https://github.com/X-yl
Reviewed-by: https://github.com/linusg

Userland/Libraries/LibIMAP/Parser.cpp

@@ -716,12 +716,12 @@ FetchCommand::DataItem Parser::parse_fetch_data_item()
             consume("]");
         } else if (is_ascii_digit(section_type[0])) {
             data_item.section->type = FetchCommand::DataItem::SectionType::Parts;
-            data_item.section->parts = Vector<int>();
+            data_item.section->parts = Vector<unsigned>();
 
             while (!try_consume("]")) {
                 auto num = parse_number();
                 if (num != (unsigned)-1) {
-                    data_item.section->parts->append((int)num);
+                    data_item.section->parts->append(num);
                     continue;
                 }
                 auto atom = parse_atom();