fix EditController._ordered_formparams method in case some mandatory relation isn't specified
If you have an HTML form which doesn't carry information about some mandatory
relation (maybe because this relation is set by a hook), you ends up with a
KeyError when the form is posted.
Using a get instead of subscription protocol fixes the problem.
Closes #5481617.
[MESSAGES CONTROL]
disable-msg = C0301
[VARIABLES]
# Enable / disable this checker
enable-variables = yes
additional-builtins = _, display_name
[BASIC]
required-attributes=
attr-rgx = (w|[a-z_][a-z0-9_]{2,30})
variable-rgx = (w|[a-z_][a-z0-9_]{2,30})$
argument-rgx = (w|[a-z_][a-z0-9_]{2,30})$
[TYPECHECK]
generated-members=debug,info,notice,warning,error,critical,exception