Fix one unretained dictionary usage in CPDF_DIB

Code appears perfectly safe at the moment, but GetImageParam() is
already returning a retained reference, so hold on to it.

Change-Id: Ifd607ad71b082fca50895da5b6b34973a261db8a
Reviewed-on: https://pdfium-review.googlesource.com/c/pdfium/+/100232
Reviewed-by: Lei Zhang <thestig@chromium.org>
Auto-Submit: Tom Sepez <tsepez@chromium.org>
Commit-Queue: Lei Zhang <thestig@chromium.org>
diff --git a/core/fpdfapi/page/cpdf_dib.cpp b/core/fpdfapi/page/cpdf_dib.cpp
index c55aa58..dec1514 100644
--- a/core/fpdfapi/page/cpdf_dib.cpp
+++ b/core/fpdfapi/page/cpdf_dib.cpp
@@ -468,7 +468,7 @@
   }
 
   pdfium::span<const uint8_t> src_span = m_pStreamAcc->GetSpan();
-  const CPDF_Dictionary* pParams = m_pStreamAcc->GetImageParam();
+  RetainPtr<const CPDF_Dictionary> pParams = m_pStreamAcc->GetImageParam();
   if (decoder == "CCITTFaxDecode") {
     m_pDecoder = CreateFaxDecoder(src_span, m_Width, m_Height, pParams);
   } else if (decoder == "FlateDecode") {