Re-enable warning 4701 for GN (re-land)

Remove one left warning from GN Release build.

Review URL: https://codereview.chromium.org/1904473003
diff --git a/BUILD.gn b/BUILD.gn
index 026ffc5..c54d57f 100644
--- a/BUILD.gn
+++ b/BUILD.gn
@@ -44,7 +44,6 @@
   if (is_win) {
     cflags += [
       "/wd4267",
-      "/wd4701",
     ]
   }
 
diff --git a/core/fpdfdoc/doc_form.cpp b/core/fpdfdoc/doc_form.cpp
index d356a5c..7c81f0e 100644
--- a/core/fpdfdoc/doc_form.cpp
+++ b/core/fpdfdoc/doc_form.cpp
@@ -416,7 +416,7 @@
 CFX_ByteString CPDF_InterForm::GetNativeFont(uint8_t charSet, void* pLogFont) {
   CFX_ByteString csFontName;
 #if _FXM_PLATFORM_ == _FXM_PLATFORM_WINDOWS_
-  LOGFONTA lf;
+  LOGFONTA lf = {};
   FX_BOOL bRet;
   if (charSet == ANSI_CHARSET) {
     csFontName = "Helvetica";