R1:6f7147376f87

Parse "multipart/form-data" bodies even if "enable_post_data_reading" is on

Summary:
Ref T4369. During T13507, I set my "max_post_size" to a very small value, like 7 (i.e., 7 bytes). This essentially disables "enable_post_data_reading" even if the setting is technically on.

This breaks forms which use "multipart/form-data", which are rare but not nonexistent. Notably, forms in Config use this setting (because of `ui.header` stuff?) although perhaps they should not or no longer need to.

This can be fixed…