pools: add more name validations.

These validations should never fail because normalize_name strips
leading/trailing underscores, consecutive underscores, and unicode
whitespace.

app/models/pool.rb

@@ -325,6 +325,14 @@ class Pool < ApplicationRecord
       errors[:name] << "cannot contain commas"
     when /\*/
       errors[:name] << "cannot contain asterisks"
+    when /\A_/
+      errors[:name] << "cannot begin with an underscore"
+    when /_\z/
+      errors[:name] << "cannot end with an underscore"
+    when /__/
+      errors[:name] << "cannot contain consecutive underscores"
+    when /[^[:graph:]]/
+      errors[:name] << "cannot contain non-printable characters"
     when ""
       errors[:name] << "cannot be blank"
     when /\A[0-9]+\z/