Cleanup env variable names

This CL cleans up any old m_pEnv variables to
be correctly named m_pFormFillEnv.

Review-Url: https://codereview.chromium.org/2412523002
diff --git a/fpdfsdk/formfiller/cffl_checkbox.cpp b/fpdfsdk/formfiller/cffl_checkbox.cpp
index 64981f0..8b5a97c 100644
--- a/fpdfsdk/formfiller/cffl_checkbox.cpp
+++ b/fpdfsdk/formfiller/cffl_checkbox.cpp
@@ -49,8 +49,8 @@
       FX_BOOL bReset = FALSE;
       FX_BOOL bExit = FALSE;
       CPDFSDK_Annot::ObservedPtr pObserved(m_pWidget);
-      m_pEnv->GetInteractiveFormFiller()->OnButtonUp(&pObserved, pPageView,
-                                                     bReset, bExit, nFlags);
+      m_pFormFillEnv->GetInteractiveFormFiller()->OnButtonUp(
+          &pObserved, pPageView, bReset, bExit, nFlags);
       if (!pObserved) {
         m_pWidget = nullptr;
         return TRUE;