Fix handling of unspecified <format> precision

Author: mborland

include/boost/decimal/format.hpp

@@ -42,7 +42,7 @@ constexpr auto parse_impl(ParseContext &ctx)
 {
     auto sign_character = format_sign_option::minus;
     auto it {ctx.begin()};
-    int ctx_precision = 6;
+    int ctx_precision = -1;
     boost::decimal::chars_format fmt = boost::decimal::chars_format::general;
     bool is_upper = false;
     int padding_digits = 0;
@@ -207,7 +207,15 @@ struct formatter<T>
             // LCOV_EXCL_STOP
         }
 
-        const auto r = to_chars(buffer_front, buffer.data() + buffer.size(), v, fmt, ctx_precision);
+        boost::decimal::to_chars_result r {};
+        if (ctx_precision != -1)
+        {
+            r = to_chars(buffer_front, buffer.data() + buffer.size(), v, fmt, ctx_precision);
+        }
+        else
+        {
+            r = to_chars(buffer_front, buffer.data() + buffer.size(), v, fmt);
+        }
 
         std::string s(buffer.data(), static_cast<std::size_t>(r.ptr - buffer.data()));