fix #5260 as suggested by reporter

ChangeLog

@@ -1,3 +1,7 @@
+Mon Jan 29 17:33:54 CET 2018
+	Fix deadlock when failing to prepare chunked response
+	(#5260). -CG/ghaderer
+
 Thu Jan  4 12:24:33 CET 2018
 	Fix __clang_major__ related warnings for non-clang
 	compilers reported by Tim on the mailinglist. -CG

src/include/microhttpd.h

@@ -126,7 +126,7 @@ typedef intptr_t ssize_t;
  * Current version of the library.
  * 0x01093001 = 1.9.30-1.
  */
-#define MHD_VERSION 0x00095800
+#define MHD_VERSION 0x00095801
 
 /**
  * MHD-internal return code for "YES".

src/microhttpd/connection.c

@@ -1155,6 +1155,7 @@ try_ready_chunked_body (struct MHD_Connection *connection)
           size /= 2;
           if (size < 128)
             {
+              MHD_mutex_unlock_chk_ (&response->mutex);
               /* not enough memory */
               CONNECTION_CLOSE_ERROR (connection,
 				      _("Closing connection (out of memory)\n"));
@@ -1200,6 +1201,7 @@ try_ready_chunked_body (struct MHD_Connection *connection)
     {
       /* error, close socket! */
       response->total_size = connection->response_write_position;
+      MHD_mutex_unlock_chk_ (&response->mutex);
       CONNECTION_CLOSE_ERROR (connection,
 			      _("Closing connection (application error generating response)\n"));
       return MHD_NO;
@@ -1218,6 +1220,7 @@ try_ready_chunked_body (struct MHD_Connection *connection)
   if (0 == ret)
     {
       connection->state = MHD_CONNECTION_CHUNKED_BODY_UNREADY;
+      MHD_mutex_unlock_chk_ (&response->mutex);
       return MHD_NO;
     }
   if (ret > 0xFFFFFF)
@@ -3593,7 +3596,7 @@ MHD_connection_handle_idle (struct MHD_Connection *connection)
                 socket_start_no_buffering (connection);
               continue;
             }
-          MHD_mutex_unlock_chk_ (&connection->response->mutex);
+          /* mutex was already unlocked by try_ready_chunked_body */
           break;
         case MHD_CONNECTION_BODY_SENT:
           if (MHD_NO == build_header_response (connection))