Make down-conversion explicit from CFX_Widetring to CFX_WideStringC.

Companion to https://codereview.chromium.org/1853233002

BUG=

Review URL: https://codereview.chromium.org/1857073002
diff --git a/fpdfsdk/javascript/PublicMethods.cpp b/fpdfsdk/javascript/PublicMethods.cpp
index b928aab..308163d 100644
--- a/fpdfsdk/javascript/PublicMethods.cpp
+++ b/fpdfsdk/javascript/PublicMethods.cpp
@@ -1219,11 +1219,11 @@
   else if (sTemp.Compare(L"Dec") == 0)
     nMonth = 12;
 
-  int nDay = FX_atof(wsArray[2]);
-  int nHour = FX_atof(wsArray[3]);
-  int nMin = FX_atof(wsArray[4]);
-  int nSec = FX_atof(wsArray[5]);
-  int nYear = FX_atof(wsArray[7]);
+  int nDay = FX_atof(wsArray[2].AsWideStringC());
+  int nHour = FX_atof(wsArray[3].AsWideStringC());
+  int nMin = FX_atof(wsArray[4].AsWideStringC());
+  int nSec = FX_atof(wsArray[5].AsWideStringC());
+  int nYear = FX_atof(wsArray[7].AsWideStringC());
   double dRet = JS_MakeDate(JS_MakeDay(nYear, nMonth - 1, nDay),
                             JS_MakeTime(nHour, nMin, nSec, 0));
   if (JS_PortIsNan(dRet))
@@ -1726,7 +1726,7 @@
             CFX_WideString trimmed = pFormField->GetValue();
             trimmed.TrimRight();
             trimmed.TrimLeft();
-            dTemp = FX_atof(trimmed);
+            dTemp = FX_atof(trimmed.AsWideStringC());
           } break;
           case FIELDTYPE_PUSHBUTTON: {
             dTemp = 0.0;
@@ -1740,7 +1740,7 @@
                   CFX_WideString trimmed = pFormCtrl->GetExportValue();
                   trimmed.TrimRight();
                   trimmed.TrimLeft();
-                  dTemp = FX_atof(trimmed);
+                  dTemp = FX_atof(trimmed.AsWideStringC());
                   break;
                 }
               }
@@ -1751,7 +1751,7 @@
               CFX_WideString trimmed = pFormField->GetValue();
               trimmed.TrimRight();
               trimmed.TrimLeft();
-              dTemp = FX_atof(trimmed);
+              dTemp = FX_atof(trimmed.AsWideStringC());
             }
           } break;
           default: