[NDB_BVL_Instrument_LINST] - fix (aces#9487)

Fix

PHP Fatal error: Uncaught TypeError: substr(): Argument #2 ($offset)
must be of type int, false given in
/var/www/Loris/php/libraries/NDB_BVL_Instrument_LINST.class.inc:172

from the BMI instrument.

php/libraries/NDB_BVL_Instrument_LINST.class.inc

@@ -167,7 +167,8 @@ class NDB_BVL_Instrument_LINST extends \NDB_BVL_Instrument
                         //If this is an OR rule using two different controllers
                         //explode it at the pipe.
                         //ex: q_1{@}=={@}yes|q_2{@}=={@}yes
-                        if (stristr(substr($rule, strpos($rule, "|")), "{@}")) {
+                        $s_r = strpos($rule, "|");
+                        if ($s_r !== false && stristr(substr($rule, $s_r), "{@}")) {
                             $rules_array = explode("|", $rule);
                         } else {
                             //Otherwise its a regular rule.  ex: q_1{@}=={@}yes