linux+callstack: Fix failing callstack

The callstack fails if a kernel trace which has the same host id is opened alongside
the ust trace and it was taken without containing the thread ids of the ust trace.
Signed-off-by: Arnaud Fiorini <[email protected]>

Author: arfio

analysis/org.eclipse.tracecompass.analysis.os.linux.core/src/org/eclipse/tracecompass/analysis/os/linux/core/kernel/KernelThreadInformationProvider.java

@@ -617,6 +617,9 @@ private static Map<Integer, String> getQuarkToThreadIds(KernelAnalysisModule mod
         Map<Integer, String> quarkToThreadIds = new HashMap<>();
         for (Integer threadId : threadIds) {
             int threadQuark = ss.optQuarkAbsolute(Attributes.THREADS, threadId.toString());
+            if (threadQuark == ITmfStateSystem.INVALID_ATTRIBUTE) {
+                continue;
+            }
             quarkToThreadIds.put(threadQuark, threadId.toString());
             int syscallQuark = ss.optQuarkRelative(threadQuark, Attributes.SYSTEM_CALL);
             if (syscallQuark != ITmfStateSystem.INVALID_ATTRIBUTE) {