Ajax: Allow `processData: true` even for binary data

Ajax: Allow `processData: true` even for binary data

The way gh-5197 implemented binary data handling, `processData`
was being explicitly set to `false`. This is expected but it made
it impossible to override it to `true`. The new logic will only
set `processData` to `false` if it wasn't explicitly passed
in original options.

Closes gh-5205
Ref gh-5197