Missing validation of rack reservation positions

[candlerb]

NetBox version

v2.11.10

Python version

3.6

Steps to Reproduce

1. Open a rack, click on "add reservation"
2. (Wrongly) enter the position as "U44" instead of "44"

Expected Behavior

A form validation error, allowing the field to be edited and resubmitted

Observed Behavior

An exception is raised:

ValueError at /dcim/rack-reservations/add/
invalid literal for int() with base 10: 'U44'