Revert "Revert "Cleanup some numeric code.""

core/src/fxcrt/fx_basic_wstring.cpp

Index: core/src/fxcrt/fx_basic_wstring.cpp
diff --git a/core/src/fxcrt/fx_basic_wstring.cpp b/core/src/fxcrt/fx_basic_wstring.cpp
index c097e1fc0923fcc3cec68cd7b254fb27029b8f17..c10ee67eed997cfb5e85da97b3059bd130660829 100644
--- a/core/src/fxcrt/fx_basic_wstring.cpp
+++ b/core/src/fxcrt/fx_basic_wstring.cpp
@@ -5,6 +5,7 @@
 // Original code copyright 2014 Foxit Software Inc. http://www.foxitsoftware.com
 
 #include <stddef.h>  // For offsetof().
+#include <cctype>
 
 #include "../../include/fxcrt/fx_basic.h"
 #include "../../../third_party/base/numerics/safe_math.h"
@@ -765,7 +766,7 @@ void CFX_WideString::FormatV(const FX_WCHAR* lpszFormat, va_list argList) {
     }
     if (nWidth == 0) {
       nWidth = FXSYS_wtoi(lpsz);
-      for (; *lpsz != 0 && (*lpsz) <= '9' && (*lpsz) >= '0'; lpsz++)
+      for (; *lpsz != 0 && std::isdigit(*lpsz); lpsz++)
         ;
     }
     if (nWidth < 0 || nWidth > 128 * 1024) {
@@ -781,7 +782,7 @@ void CFX_WideString::FormatV(const FX_WCHAR* lpszFormat, va_list argList) {
         lpsz++;
       } else {
         nPrecision = FXSYS_wtoi(lpsz);
-        for (; *lpsz != 0 && (*lpsz) >= '0' && (*lpsz) <= '9'; lpsz++)
+        for (; *lpsz != 0 && std::isdigit(*lpsz); lpsz++)
           ;
       }
     }