V2 input crash when offset is unspecified

[ccorn]

The following simple program crashes (SIGSEGV) with Boost 1.71.0 when reaching in >> tp:

#define BOOST_CHRONO_VERSION 2
#include <boost/chrono.hpp>
#include <boost/chrono/io/time_point_io.hpp>
#include <cassert>      // assert
#include <sstream>      // std::istringstream
#include <string>       // std::string

int main() {
    namespace bc = boost::chrono;

    std::istringstream in("2019-09-16 13:16:31.539");   // missing offset
    // bc::timezone_io_saver tzs(in, bc::timezone::local); // try this as well
    bc::system_clock::time_point tp;

    in >> tp;           // crashes with default format
    assert(in.eof());
    assert(in.fail());
    assert(!in.bad());
    return 0;
}

The following diff prevents the crash and fulfills the asserts:

--- boost/chrono/io/time_point_io.hpp.orig	2019-08-14 14:02:21.000000000 +0200
+++ boost/chrono/io/time_point_io.hpp	2019-09-16 20:13:47.435303802 +0200
@@ -1152,6 +1152,11 @@ namespace boost
             }
             It i(is);
             It eof;
+            if (i == eof)
+            {
+              err |= std::ios_base::failbit;
+              goto exit;
+            }
             c = *i;
             if (++i == eof || c != ' ')
             {

[viboes]

A PR is more than welcome.