XFA: Fix a crashier in SetFocus()

public/fpdf_formfill.h

Index: public/fpdf_formfill.h
diff --git a/public/fpdf_formfill.h b/public/fpdf_formfill.h
index b3bbb9280c0e4d82ee0cd120761c29b4d5e28f86..5521fb4859acccdc5965ecfa9da97a702eecc0cd 100644
--- a/public/fpdf_formfill.h
+++ b/public/fpdf_formfill.h
@@ -1011,6 +1011,29 @@ typedef struct _FPDF_FORMFILLINFO {
   *       TRUE indicates success, otherwise FALSE.
   **/
   FPDF_BOOL   (*FFI_PutRequestURL)(struct _FPDF_FORMFILLINFO* pThis, FPDF_WIDESTRING wsURL, FPDF_WIDESTRING wsData, FPDF_WIDESTRING wsEncode);
+
+  /**
+  * Method: FFI_PageEvent
+  *           This method will notify applications when a page is deleted or
+  *removed.
+  * Interface Version:
+  *           1
+  * Implementation Required:
+  *           yes
+  * Parameters:
+  *       pThis           -   Pointer to the interface structure itself.
+  *       iPageIndex      -   The index of which page is modified.
+  *       iEventType      -   Type of events. It can be one of
+  *the following marcos:
+  *                           1. FXFA_PAGEVIEWEVENT_POSTADDED
+  *                           2. FXFA_PAGEVIEWEVENT_POSTREMOVED
+  * Return value:
+  *       None.
+  **/
+  void (*FFI_PageEvent)(struct _FPDF_FORMFILLINFO* pThis,
+                        int iPageIndex,
+                        int iEventType);
+
 #endif  // PDF_ENABLE_XFA
 
 } FPDF_FORMFILLINFO;