Bug 570745 - [Generic Editor] Fix content type detection

Change-Id: I3e775cbd1dcaa1bec406ba0955aaaaa78a568e4b
Signed-off-by: Mickael Istria <mistria@redhat.com>
diff --git a/org.eclipse.ui.genericeditor/src/org/eclipse/ui/internal/genericeditor/ExtensionBasedTextViewerConfiguration.java b/org.eclipse.ui.genericeditor/src/org/eclipse/ui/internal/genericeditor/ExtensionBasedTextViewerConfiguration.java
index 2ef26c1..1d77bf7 100644
--- a/org.eclipse.ui.genericeditor/src/org/eclipse/ui/internal/genericeditor/ExtensionBasedTextViewerConfiguration.java
+++ b/org.eclipse.ui.genericeditor/src/org/eclipse/ui/internal/genericeditor/ExtensionBasedTextViewerConfiguration.java
@@ -111,7 +111,7 @@
 		}
 		if (fileName == null) {
 			IDocument viewerDocument = viewer.getDocument();
-			if (document != null) {
+			if (viewerDocument != null) {
 				ITextFileBuffer buffer = FileBuffers.getTextFileBufferManager().getTextFileBuffer(viewerDocument);
 				if (buffer != null) {
 					fileName = buffer.getLocation().lastSegment();