Fix an additional space in help generated (#377)

Author: soumeh01

include/cxxopts.hpp

@@ -2742,7 +2742,12 @@ Options::help(const std::vector<std::string>& help_groups, bool print_usage) con
   String result = m_help_string;
   if(print_usage)
   {
-    result+= "\nUsage:\n  " + toLocalString(m_program) + " " + toLocalString(m_custom_help);
+    result+= "\nUsage:\n  " + toLocalString(m_program);
+  }
+
+  if (!m_custom_help.empty())
+  {
+    result += " " + toLocalString(m_custom_help);
   }
 
   if (!m_positional.empty() && !m_positional_help.empty()) {

test/options.cpp

@@ -918,3 +918,27 @@ TEST_CASE("Iterator", "[iterator]") {
 
   REQUIRE(++iter == result.end());
 }
+
+TEST_CASE("No Options help", "[options]")
+{
+  std::vector<std::string> positional;
+
+  cxxopts::Options options("test", "test no options help");
+
+  // explicitly setting custom help empty to overwrite
+  // default "[OPTION...]" when there are no options
+  options.positional_help("<posArg1>...<posArgN>")
+    .custom_help("")
+    .add_options()
+      ("positional", "", cxxopts::value<std::vector<std::string>>(positional));
+
+  Argv av({"test", "posArg1", "posArg2", "posArg3"});
+
+  auto argc   = av.argc();
+  auto** argv = av.argv();
+
+  options.parse_positional({"positional"});
+
+  CHECK_NOTHROW(options.parse(argc, argv));
+  CHECK(options.help().find("test <posArg1>...<posArgN>") != std::string::npos);
+}