Check result of GetEventParam() in CJX_Form::recalculate().

All other callers are already checking for a NULL return.

Bug: pdfium:1254
Change-Id: I1848554d237c6301d78893931c5f99b1d9aacd1b
Reviewed-on: https://pdfium-review.googlesource.com/c/pdfium/+/51730
Reviewed-by: Lei Zhang <thestig@chromium.org>
Commit-Queue: Tom Sepez <tsepez@chromium.org>

fxjs/xfa/cjx_form.cpp

diff --git a/fxjs/xfa/cjx_form.cpp b/fxjs/xfa/cjx_form.cpp
index 0a65286..41f7e45 100644
--- a/fxjs/xfa/cjx_form.cpp
+++ b/fxjs/xfa/cjx_form.cpp
@@ -82,8 +82,8 @@
     const std::vector<v8::Local<v8::Value>>& params) {
   CXFA_EventParam* pEventParam =
       GetDocument()->GetScriptContext()->GetEventParam();
-  if (pEventParam->m_eType == XFA_EVENT_Calculate ||
-      pEventParam->m_eType == XFA_EVENT_InitCalculate) {
+  if (pEventParam && (pEventParam->m_eType == XFA_EVENT_Calculate ||
+                      pEventParam->m_eType == XFA_EVENT_InitCalculate)) {
     return CJS_Result::Success();
   }
   if (params.size() != 1)