Use strto* instead of std::sto*

std::sto* throw if the string does not start with a number, but doesn't throw
if it's not just a number. No idea who invented such behaviour ¯\_(ツ)_/¯

json11.cpp

@@ -214,9 +214,30 @@ class JsonString final : public Value<Json::STRING, string> {
     string as_string() const { return m_value; }
     const string &string_value() const override { return m_value; }
     bool bool_value() const override { return m_value != "" && m_value != "0"; }
-    double number_value() const override { size_t pos = 0; double v = std::stod(m_value, &pos); if (pos < m_value.length()) { v = 0; } return v; }
-    int64_ int64_value() const override { size_t pos = 0; int64_ v = std::stoll(m_value, &pos); if (pos < m_value.length()) { v = 0; } return v; }
-    uint64_ uint64_value() const override { size_t pos = 0; uint64_ v = std::stoull(m_value, &pos); if (pos < m_value.length()) { v = 0; } return v; }
+    double number_value() const override
+    {
+        char *endptr = NULL;
+        double v = strtod(m_value.c_str(), &endptr);
+        if (endptr < m_value.c_str()+m_value.length())
+            v = 0;
+        return v;
+    }
+    int64_ int64_value() const override
+    {
+        char *endptr = NULL;
+        int64_ v = strtoll(m_value.c_str(), &endptr, 10);
+        if (endptr < m_value.c_str()+m_value.length())
+            v = 0;
+        return v;
+    }
+    uint64_ uint64_value() const override
+    {
+        char *endptr = NULL;
+        uint64_ v = strtoull(m_value.c_str(), &endptr, 10);
+        if (endptr < m_value.c_str()+m_value.length())
+            v = 0;
+        return v;
+    }
 public:
     explicit JsonString(const string &value) : Value(value) {}
     explicit JsonString(string &&value)      : Value(move(value)) {}