Take advantage of implicit std::unique_ptr<>(nulltpr_t) ctor.

core/fpdfapi/font/cpdf_font.cpp

Index: core/fpdfapi/font/cpdf_font.cpp
diff --git a/core/fpdfapi/font/cpdf_font.cpp b/core/fpdfapi/font/cpdf_font.cpp
index d39f752a8b7276ed115fcc48061ee39824d76b5a..c5da4ea519634946d0373b995d485f4b7b330f73 100644
--- a/core/fpdfapi/font/cpdf_font.cpp
+++ b/core/fpdfapi/font/cpdf_font.cpp
@@ -343,7 +343,7 @@ std::unique_ptr<CPDF_Font> CPDF_Font::Create(CPDF_Document* pDoc,
   pFont->m_pFontDict = pFontDict;
   pFont->m_pDocument = pDoc;
   pFont->m_BaseFont = pFontDict->GetStringFor("BaseFont");
-  return pFont->Load() ? std::move(pFont) : std::unique_ptr<CPDF_Font>();
+  return pFont->Load() ? std::move(pFont) : nullptr;
 }
 
 uint32_t CPDF_Font::GetNextChar(const FX_CHAR* pString,