tmf.ui: Gracefully handle invalid tar import operations

A tar.gz file may have an invalid tar file in the gzip. The
getNextEntry would return null in such a case. This performs
that null check in order to validate the tar and avoid a user-
facing NPE.

Change-Id: I28ae7c787d77a0f1c9136264cfc678d7e52cda1a
Signed-off-by: Matthew Khouzam <matthew.khouzam@ericsson.com>
Reviewed-on: https://git.eclipse.org/r/87247
Reviewed-by: Hudson CI
Reviewed-by: Marc-André Laperle <marc-andre.laperle@ericsson.com>
Tested-by: Marc-André Laperle <marc-andre.laperle@ericsson.com>
(cherry picked from commit 6facaeb6ec0e729c457abb780fbc05995c0061cd)
Reviewed-on: https://git.eclipse.org/r/87272
diff --git a/tmf/org.eclipse.tracecompass.tmf.ui/src/org/eclipse/tracecompass/internal/tmf/ui/project/wizards/importtrace/TarFile.java b/tmf/org.eclipse.tracecompass.tmf.ui/src/org/eclipse/tracecompass/internal/tmf/ui/project/wizards/importtrace/TarFile.java
index 3647aa1..ea38302 100644
--- a/tmf/org.eclipse.tracecompass.tmf.ui/src/org/eclipse/tracecompass/internal/tmf/ui/project/wizards/importtrace/TarFile.java
+++ b/tmf/org.eclipse.tracecompass.tmf.ui/src/org/eclipse/tracecompass/internal/tmf/ui/project/wizards/importtrace/TarFile.java
@@ -63,7 +63,7 @@
         entryEnumerationStream = new TarArchiveInputStream(fInputStream);
         try {
             curEntry = (TarArchiveEntry) entryEnumerationStream.getNextEntry();
-            if (!curEntry.isCheckSumOK()) {
+            if (curEntry == null || !curEntry.isCheckSumOK()) {
                 throw new IOException("Error detected parsing initial entry header"); //$NON-NLS-1$
             }
         } catch (IOException e) {