Regression: isAnyCharRequiredQuoting() is broken on Windows in JsonCpp 1.9.3 for some locales.

[TheStormN]

Describe the bug
The tab character is not escaped on Windows with various locales. This bug is a regression in 1.9.3, it is not present in 1.9.2.

To Reproduce
Steps to reproduce the behavior:

setlocale(LC_ALL, "English_United States.1252");

Json::Value result(Json::objectValue);
result["test"] = "\tTest123";

Json::StreamWriterBuilder builder;
assert(Json::writeString(builder, result) == "{\"test\":\"\\tTest123\"}" );

Expected behavior
The tab character should be escaped.

Desktop:

• OS: Windows 10 1909
• Meson version - Using Conan
• Ninja version - Using Conan

Additional context
isAnyCharRequiredQuoting() uses std::isprint() which gives different results on Windows. The version of that function in 1.9.2 was working properly. Perhaps you can just revert it?

Update: It seems that the locale does not matter, to reproduce the bug you only need to have \t as a special character among the normal string.

Update 2: It seems that the locale does matter. Had to restart the PC to get proper results after changing the locale several times.

[BillyDonahue]

Wait, are you saying std::isprint('\t') returns true on Windows?!
Let's get an answer to that specific question?

[TheStormN]

@BillyDonahue Yeah, I had hard times debugging that, but it seems that it depends on the locale. For example English_United States.1252 does return true for \t. I've updated my issue description.

So, basically it depends on the users system-wide locale if this will work or not. I've provided a easy to reproduce version with setting the locale by using C++ code.