Handle Pdfium errors

... and factor out common code from PdfEditor and PdfRenderer to
PdfUtils.h

Change-Id: If193579d8fccb55a3c2a7e1fa3c935ce410a17c2
diff --git a/core/jni/Android.mk b/core/jni/Android.mk
index 60e888d..93ff637 100644
--- a/core/jni/Android.mk
+++ b/core/jni/Android.mk
@@ -138,6 +138,7 @@
     android/graphics/pdf/PdfDocument.cpp \
     android/graphics/pdf/PdfEditor.cpp \
     android/graphics/pdf/PdfRenderer.cpp \
+    android/graphics/pdf/PdfUtils.cpp \
     android_media_AudioRecord.cpp \
     android_media_AudioSystem.cpp \
     android_media_AudioTrack.cpp \