Bug 561534 - NPE in AdditionalInfoController.computeInformation

The code is executed asynchronously, it may happen that the proposal
shell is already dismissed by user, so we simply don't need to do
anything.

Change-Id: I718bda2e8ff7f73830c037c875cbc37328ceaa7d
Signed-off-by: Andrey Loskutov <loskutov@gmx.de>
diff --git a/org.eclipse.jface.text/src/org/eclipse/jface/text/contentassist/AdditionalInfoController.java b/org.eclipse.jface.text/src/org/eclipse/jface/text/contentassist/AdditionalInfoController.java
index a4c43e6..5dab861 100644
--- a/org.eclipse.jface.text/src/org/eclipse/jface/text/contentassist/AdditionalInfoController.java
+++ b/org.eclipse.jface.text/src/org/eclipse/jface/text/contentassist/AdditionalInfoController.java
@@ -532,6 +532,10 @@
 
 	@Override
 	protected void computeInformation() {
+		if (fProposalTable == null || fProposalTable.isDisposed()) {
+			return;
+		}
+
 		if (fProposal instanceof ICompletionProposalExtension3)
 			setCustomInformationControlCreator(((ICompletionProposalExtension3) fProposal).getInformationControlCreator());
 		else