minor #6759 Fix tense and sentence length (aalaap)

This PR was submitted for the 2.8 branch but it was merged into the 2.7 branch instead (closes #6759).

Discussion
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Fix tense and sentence length

Changed past-perfect and present mixture to use just the present tense and added a comma.

Before:
> If the user had submitted an invalid username or password, this controller reads the form submission error from the security system so that it can be displayed back to the user.

After:
> If the user submits an invalid username or password, this controller reads the form submission error from the security system so, that it can be displayed back to the user.

Commits
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fd2d9c1 Fix tense and sentence length

Author: weaverryan

security/form_login_setup.rst

@@ -171,9 +171,9 @@ form::
 
 Don't let this controller confuse you. As you'll see in a moment, when the
 user submits the form, the security system automatically handles the form
-submission for you. If the user had submitted an invalid username or password,
-this controller reads the form submission error from the security system so
-that it can be displayed back to the user.
+submission for you. If the user submits an invalid username or password,
+this controller reads the form submission error from the security system,
+so that it can be displayed back to the user.
 
 In other words, your job is to *display* the login form and any login errors
 that may have occurred, but the security system itself takes care of checking