Fixed a crash occurring when a thread does not have a stack trace.

src/main/scala/leon/frontends/scalac/CodeExtraction.scala

@@ -1729,7 +1729,9 @@ trait CodeExtraction extends ASTExtractors {
               val typea1 = a1.getType
               val typea2 = a2.map(_.getType).mkString(",")
               val sa2 = a2.mkString(",")
+              try {
               println(Thread.currentThread().getStackTrace.take(5).mkString("\n"))
+              } catch { case e: Throwable => }
               outOfSubsetError(tr, "Unknown call to " + name + s" on $a1 ($typea1) with arguments $sa2 of type $typea2")
           }