Fix abort above FPDFPage_Flatten

fpdfsdk/cpdfsdk_formfillenvironment.h

Index: fpdfsdk/cpdfsdk_formfillenvironment.h
diff --git a/fpdfsdk/cpdfsdk_formfillenvironment.h b/fpdfsdk/cpdfsdk_formfillenvironment.h
index 24380197072c30a75ce9056979bef586fa5bc864..e41dec6978c71eccaa0091941b1db34e45271fa4 100644
--- a/fpdfsdk/cpdfsdk_formfillenvironment.h
+++ b/fpdfsdk/cpdfsdk_formfillenvironment.h
@@ -213,7 +213,6 @@ class CPDFSDK_FormFillEnvironment
   std::unique_ptr<CPDFSDK_ActionHandler> m_pActionHandler;
   std::unique_ptr<IJS_Runtime> m_pJSRuntime;
   FPDF_FORMFILLINFO* const m_pInfo;
-  std::map<UnderlyingPageType*, std::unique_ptr<CPDFSDK_PageView>> m_pageMap;
   std::unique_ptr<CPDFSDK_InterForm> m_pInterForm;
   CPDFSDK_Annot::ObservedPtr m_pFocusAnnot;
   UnderlyingDocumentType* m_pUnderlyingDoc;
@@ -221,6 +220,9 @@ class CPDFSDK_FormFillEnvironment
   std::unique_ptr<CFX_SystemHandler> m_pSysHandler;
   bool m_bChangeMask;
   bool m_bBeingDestroyed;
+
+  // Must be destroyed first.
+  std::map<UnderlyingPageType*, std::unique_ptr<CPDFSDK_PageView>> m_pageMap;
 };
 
 #endif  // FPDFSDK_CPDFSDK_FORMFILLENVIRONMENT_H_