[FIR] Fix FindReferencePositioningStrategy for light tree

There was a problem which causes to lookup for assign token inside
  functions from arguments of call

core/util.runtime/src/org/jetbrains/kotlin/utils/addToStdlib.kt

@@ -178,6 +178,7 @@ inline fun <T, R> Iterable<T>.same(extractor: (T) -> R): Boolean {
 }
 
 inline fun <R> runIf(condition: Boolean, block: () -> R): R? = if (condition) block() else null
+inline fun <R> runUnless(condition: Boolean, block: () -> R): R? = if (condition) null else block()
 
 inline fun <T, R> Collection<T>.foldMap(transform: (T) -> R, operation: (R, R) -> R): R {
     val iterator = iterator()