Don't send notif mail when updating Protected account's Access Level

Prior to this, Mantis would effectively not update the protected user
account's 'Access Level' field, but would still send a notification to
the user informing them that the field was modified, causing confusion.

The confirmation message for protected account update was reworded.

Fixes #15247

lang/strings_english.txt

@@ -997,7 +997,7 @@ $s_account_reset_msg2 = 'Account password has been set to blank...';
 $s_account_unlock_msg = 'The account has been unlocked.';
 
 # manage_user_update.php
-$s_manage_user_protected_msg = 'Account protected. Access level and enabled protected. Otherwise, account has been updated...';
+$s_manage_user_protected_msg = 'Account protected; the \'Access Level\' and \'Enabled\' fields cannot be modified. Other fields were successfully updated.';
 $s_manage_user_updated_msg = 'Account successfully updated...';
 $s_email_user_updated_subject = 'Account updated';
 $s_email_user_updated_msg = 'Your account has been updated by an administrator. A list of these changes is provided below. You can update your account details and preferences at any time by visiting the following URL:';

manage_user_update.php

@@ -132,6 +132,8 @@
 	    			protected=" . db_param() . ", realname=" . db_param() . "
 	    		WHERE id=" . db_param();
 	    $query_params = Array( $c_username, $c_email, $c_protected, $c_realname, $c_user_id );
+		# Prevent e-mail notification for a change that did not happen
+		$f_access_level = $t_old_access_level;
 	} else {
 	    $query = "UPDATE $t_user_table
 	    		SET username=" . db_param() . ", email=" . db_param() . ",