Revert "Revert "Cleanup some numeric code.""

core/src/fxcrt/fx_basic_util.cpp

Index: core/src/fxcrt/fx_basic_util.cpp
diff --git a/core/src/fxcrt/fx_basic_util.cpp b/core/src/fxcrt/fx_basic_util.cpp
index 46a0dec1e538884370b92f7865aa84d1fde13722..70bbacc7e822ca963901c1cc78ccf6d55ebf1614 100644
--- a/core/src/fxcrt/fx_basic_util.cpp
+++ b/core/src/fxcrt/fx_basic_util.cpp
@@ -11,6 +11,9 @@
 #else
 #include <direct.h>
 #endif
+
+#include <cctype>
+
 CFX_PrivateData::~CFX_PrivateData() {
   ClearAll();
 }
@@ -101,13 +104,13 @@ void FX_atonum(const CFX_ByteStringC& strc, FX_BOOL& bInteger, void* pData) {
       cc++;
     }
     while (cc < len) {
-      if (str[cc] < '0' || str[cc] > '9') {
+      if (!std::isdigit(str[cc]))
         break;
-      }
+
       integer = integer * 10 + str[cc] - '0';
-      if (integer < 0) {
+      if (integer < 0)
         break;
-      }
+
       cc++;
     }
     if (bNegative) {