(http client) fix deadlock when following redirects

ixwebsocket/IXHttpClient.cpp

@@ -127,7 +127,7 @@ namespace ix
     {
         // We only have one socket connection, so we cannot
         // make multiple requests concurrently.
-        std::lock_guard<std::mutex> lock(_mutex);
+        std::lock_guard<std::recursive_mutex> lock(_mutex);
 
         uint64_t uploadSize = 0;
         uint64_t downloadSize = 0;

ixwebsocket/IXHttpClient.h

@@ -103,7 +103,9 @@ namespace ix
         std::thread _thread;
 
         std::unique_ptr<Socket> _socket;
-        std::mutex _mutex; // to protect accessing the _socket (only one socket per client)
+        std::recursive_mutex _mutex; // to protect accessing the _socket (only one socket per client)
+                                     // the mutex needs to be recursive as this function might
+                                     // be called recursively to follow HTTP redirections
 
         SocketTLSOptions _tlsOptions;
 

ixwebsocket/IXWebSocketVersion.h

@@ -6,4 +6,4 @@
 
 #pragma once
 
-#define IX_WEBSOCKET_VERSION "9.7.8"
+#define IX_WEBSOCKET_VERSION "9.7.9"