pdfviewer: more prerequired work to have examples working for transparency work items.

Review URL: https://codereview.chromium.org/21252003

git-svn-id: http://skia.googlecode.com/svn/trunk@10438 2bbb7eff-a529-9590-31e7-b0007b416f81
diff --git a/experimental/PdfViewer/pdfparser/native/SkNativeParsedPDF.cpp b/experimental/PdfViewer/pdfparser/native/SkNativeParsedPDF.cpp
index 3273182..597dfcd 100644
--- a/experimental/PdfViewer/pdfparser/native/SkNativeParsedPDF.cpp
+++ b/experimental/PdfViewer/pdfparser/native/SkNativeParsedPDF.cpp
@@ -123,8 +123,11 @@
     bool storeCatalog = true;
     while (xrefByteOffset >= 0) {
         const unsigned char* trailerStart = readCrossReferenceSection(fFileContent + xrefByteOffset, xrefstartKeywordLine);
-        readTrailer(trailerStart, xrefstartKeywordLine, storeCatalog, &xrefByteOffset, false);
-        storeCatalog = false;
+        xrefByteOffset = -1;
+        if (trailerStart < xrefstartKeywordLine) {
+            readTrailer(trailerStart, xrefstartKeywordLine, storeCatalog, &xrefByteOffset, false);
+            storeCatalog = false;
+        }
     }
 
     // TODO(edisonn): warn/error expect fObjects[fRefCatalogId].fGeneration == fRefCatalogGeneration