Issue #21, HTTP version mismatch crashes server

server_http.hpp

@@ -10,6 +10,7 @@
 #include <list>
 #include <map>
 #include <sstream>
+#include <stdexcept>
 #include <thread>
 #include <unordered_set>
 
@@ -762,7 +763,18 @@ namespace SimpleWeb {
                 return;
               }
             }
-            if(std::stof(response->session->request->http_version) >= 1.1) {
+
+
+						auto http_ver_string = response->session->request->http_version;
+						double http_ver_float;
+						try {
+							http_ver_float = std::stof(http_ver_string);
+						} catch (const std::invalid_argument) {
+							http_ver_float = 1.0;
+						}
+
+
+            if(http_ver_float >= 1.1) {
               auto new_session = std::make_shared<Session>(this->config.max_request_streambuf_size, response->session->connection);
               this->read(new_session);
               return;