flags can be null

Author: thurka

visualvm/sampler.truffle/src/org/graalvm/visualvm/sampler/truffle/cpu/CPUSamplerSupport.java

@@ -259,7 +259,7 @@ private void addSourceNames(Map<String,Object>[] infoMap) {
 
                 for (int i = 0; i <stack.length; i++) {
                     StackTraceElement ste = stack[i];
-                    byte flag = flags[i];
+                    byte flag = flags!=null ? flags[i] : 0;
                     File file = new File(ste.getFileName());
                     String fname = file.getName();
                     String flagSrt = "";