Correctly handle decoders in CPDF_DIBBase::ContinueLoadDIBBase().

Fix SMask rendering when the SMask is not JBIG2.

BUG=pdfium:1236

Change-Id: Ic06410f52515ede252886300d447a00ca18104db
Reviewed-on: https://pdfium-review.googlesource.com/c/50830
Commit-Queue: Lei Zhang <thestig@chromium.org>
Reviewed-by: Tom Sepez <tsepez@chromium.org>

core/fpdfapi/render/cpdf_dibbase.cpp

diff --git a/core/fpdfapi/render/cpdf_dibbase.cpp b/core/fpdfapi/render/cpdf_dibbase.cpp
index b325edb..322e76a 100644
--- a/core/fpdfapi/render/cpdf_dibbase.cpp
+++ b/core/fpdfapi/render/cpdf_dibbase.cpp
@@ -291,14 +291,16 @@
   if (m_Status == LoadState::kContinue)
     return ContinueLoadMaskDIB(pPause);
 
-  if (m_Status == LoadState::kFail)
-    return LoadState::kFail;
-
   ByteString decoder = m_pStreamAcc->GetImageDecoder();
   if (decoder == "JPXDecode")
     return LoadState::kFail;
 
-  ASSERT(decoder == "JBIG2Decode");
+  if (decoder != "JBIG2Decode")
+    return LoadState::kSuccess;
+
+  if (m_Status == LoadState::kFail)
+    return LoadState::kFail;
+
   FXCODEC_STATUS iDecodeStatus;
   CCodec_Jbig2Module* pJbig2Module = CPDF_ModuleMgr::Get()->GetJbig2Module();
   if (!m_pJbig2Context) {

testing/resources/pixel/bug_1236_expected.pdf.0.png

diff --git a/testing/resources/pixel/bug_1236_expected.pdf.0.png b/testing/resources/pixel/bug_1236_expected.pdf.0.png
index 114e34a..2020fec 100644
--- a/testing/resources/pixel/bug_1236_expected.pdf.0.png
+++ b/testing/resources/pixel/bug_1236_expected.pdf.0.png
Binary files differ