keep search-term length out of sentry
keep search-term length out of sentry

closes FOO-1306
flag=none

TEST PLAN:
  1) search for users with a term like "a"
  2) you should not get a 500, but a 400
  3) no sentry errors

Change-Id: Idb614e07dd95af6564f73c4480549bd8097167e5
Reviewed-on: https://gerrit.instructure.com/c/canvas-lms/+/254768
Tested-by: Service Cloud Jenkins <9144042a601061f88f1e1d7a1753ea3e2972119d@instructure.com>
Reviewed-by: Cody Cutrer <c4fe2b1d90ef8f2548c8aeabfa633434316f0305@instructure.com>
QA-Review: Cody Cutrer <c4fe2b1d90ef8f2548c8aeabfa633434316f0305@instructure.com>
Product-Review: Cody Cutrer <c4fe2b1d90ef8f2548c8aeabfa633434316f0305@instructure.com>

sfu/canvas-lms,sfu/canvas-lms,sfu/canvas-lms,sfu/canvas-lms,sfu/canvas-lms,sfu/canvas-lms,sfu/canvas-lms