Add fuzzing crash reproducer

Author: mborland

fuzzing/old_crashes/fuzz_snprintf/crash-da39a3ee5e6b4b0d3255bfef95601890afd80709

@@ -0,0 +1 @@
+0000000000000000000000000000000000000000

fuzzing/old_crashes/fuzz_snprintf/crash-github-1

@@ -170,6 +170,38 @@ void test_bootstrap()
     }
 }
 
+void test_fuzzer_crash()
+{
+    auto c_data = reinterpret_cast<const char*>("");
+    auto size = std::strlen(c_data);
+
+    const auto formats = std::array<boost::decimal::chars_format, 4>{boost::decimal::chars_format::general,
+                                                                     boost::decimal::chars_format::fixed,
+                                                                     boost::decimal::chars_format::scientific,
+                                                                     boost::decimal::chars_format::hex};
+
+    const auto dec32_printf_formats = std::array<const char*, 4>{"%Hg", "%Hf", "%He", "%Ha"};
+    const auto dec64_printf_formats = std::array<const char*, 4>{"%Dg", "%Df", "%De", "%Da"};
+    const auto dec128_printf_formats = std::array<const char*, 4>{"%DDg", "%DDf", "%DDe", "%DDa"};
+
+    for (std::size_t i {}; i < 4; ++i)
+    {
+        char buffer[20]; // Small enough it should overflow sometimes
+
+        boost::decimal::decimal32 f_val {};
+        boost::decimal::from_chars(c_data, c_data + size, f_val, formats[i]);
+        boost::decimal::snprintf(buffer, sizeof(buffer), dec32_printf_formats[i], f_val);
+
+        boost::decimal::decimal64 val {};
+        boost::decimal::from_chars(c_data, c_data + size, val, formats[i]);
+        boost::decimal::snprintf(buffer, sizeof(buffer), dec64_printf_formats[i], val);
+
+        boost::decimal::decimal128 ld_val {};
+        boost::decimal::from_chars(c_data, c_data + size, ld_val, formats[i]);
+        boost::decimal::snprintf(buffer, sizeof(buffer), dec128_printf_formats[i], ld_val);
+    }
+}
+
 int main()
 {
     test_bootstrap<decimal32>();
@@ -181,5 +213,7 @@ int main()
     test_locales();
     #endif
 
+    test_fuzzer_crash();
+
     return boost::report_errors();
 }