Fix segv in CFXJSE_FormCalcContext::Time2Num().

There's no reason the document-supplied third argument to TimeToNum()
has to correspond to an actual locale. If it doesn't, then continue
using the node's locale.

Bug: pdfium:1257
Change-Id: I473c4e1982af00494564011c4d6f98b89a20a61f
Reviewed-on: https://pdfium-review.googlesource.com/c/pdfium/+/77490
Reviewed-by: Daniel Hosseinian <dhoss@chromium.org>
Commit-Queue: Tom Sepez <tsepez@chromium.org>

fxjs/xfa/cfxjse_formcalc_context.cpp

diff --git a/fxjs/xfa/cfxjse_formcalc_context.cpp b/fxjs/xfa/cfxjse_formcalc_context.cpp
index dca2a66..84dfaba 100644
--- a/fxjs/xfa/cfxjse_formcalc_context.cpp
+++ b/fxjs/xfa/cfxjse_formcalc_context.cpp
@@ -2451,13 +2451,14 @@
   CXFA_Document* pDoc = ToFormCalcContext(pThis)->GetDocument();
   CXFA_LocaleMgr* pMgr = pDoc->GetLocaleMgr();
   GCedLocaleIface* pLocale = nullptr;
-  if (bsLocale.IsEmpty()) {
-    CXFA_Node* pThisNode = ToNode(pDoc->GetScriptContext()->GetThisObject());
-    pLocale = pThisNode->GetLocale();
-  } else {
+  if (!bsLocale.IsEmpty()) {
     pLocale =
         pMgr->GetLocaleByName(WideString::FromUTF8(bsLocale.AsStringView()));
   }
+  if (!pLocale) {
+    CXFA_Node* pThisNode = ToNode(pDoc->GetScriptContext()->GetThisObject());
+    pLocale = pThisNode->GetLocale();
+  }
 
   WideString wsFormat;
   if (bsFormat.IsEmpty()) {

fxjs/xfa/cfxjse_formcalc_context_embeddertest.cpp

diff --git a/fxjs/xfa/cfxjse_formcalc_context_embeddertest.cpp b/fxjs/xfa/cfxjse_formcalc_context_embeddertest.cpp
index 977f3f7..0b5ac5a 100644
--- a/fxjs/xfa/cfxjse_formcalc_context_embeddertest.cpp
+++ b/fxjs/xfa/cfxjse_formcalc_context_embeddertest.cpp
@@ -515,7 +515,9 @@
     int result;
   } tests[] = {
       // {"Time2Num(\"00:00:00 GMT\", \"HH:MM:SS Z\")", 1},
-      {"Time2Num(\"13:13:13 GMT\", \"HH:MM:SS Z\", \"fr_FR\")", 47593001}};
+      {"Time2Num(\"\", \"\", 1)", 0},  // https://crbug.com/pdfium/1257
+      {"Time2Num(\"13:13:13 GMT\", \"HH:MM:SS Z\", \"fr_FR\")", 47593001},
+  };
 
   for (size_t i = 0; i < pdfium::size(tests); ++i)
     ExecuteExpectInt32(tests[i].program, tests[i].result);