[core] Fix incorrect message/error for instrument access (#8284)

An incorrect error message was displayed on the frontend when a user did not have the permission to access an instrument.
The code was test looping on ALL permissions, but it failed when trying to do so on only ONE permission (the loop went through the instrument name and permission instead of the actual instruments objects).

Resolves #8171

php/libraries/NDB_BVL_Instrument.class.inc

@@ -362,10 +362,18 @@ abstract class NDB_BVL_Instrument extends NDB_Page
         } else { //check if user has instrument's permissions
             //is the instrument listed at all in instrumentPermissions?
             $instrumentListed = false;
-            foreach ($instrumentPermissions["instrument"] as $instrument) {
+            // get an array of instruments
+            // if one instrument, get it into an array
+            $instrumentList = Utility::asArray(
+                $instrumentPermissions["instrument"]
+            );
+            // iterate through instruments
+            foreach ($instrumentList as $instrument) {
                 if ($instrument["Test_name"] == $this->testName) {
                     $instrumentListed = true;
-                    $instrumentPerms  = Utility::asArray($instrument["permission"]);
+                    $instrumentPerms  = Utility::asArray(
+                        $instrument["permission"]
+                    );
                 }
             }