Fix UB in websocket read tests

An object returned from a function is not guaranteed not to be copied
in C++14 or earlier, using `initializer_list` removes the reliance on
RVO to work.

Signed-off-by: Damian Jarek <damian.jarek93@gmail.com>

test/beast/websocket/read2.cpp

@@ -133,7 +133,7 @@ public:
         [&](ws_type_t<deflateSupported>& ws)
         {
             put(ws.next_layer().buffer(), cbuf(
-                0x89, 0x00));
+                {0x89, 0x00}));
             bool invoked = false;
             ws.control_callback(
                 [&](frame_type kind, string_view)
@@ -155,7 +155,7 @@ public:
         [&](ws_type_t<deflateSupported>& ws)
         {
             put(ws.next_layer().buffer(), cbuf(
-                0x88, 0x00));
+                {0x88, 0x00}));
             bool invoked = false;
             ws.control_callback(
                 [&](frame_type kind, string_view)
@@ -313,7 +313,7 @@ public:
         [&](ws_type_t<deflateSupported>& ws)
         {
             w.write_raw(ws, cbuf(
-                0x8f, 0x80, 0xff, 0xff, 0xff, 0xff));
+                {0x8f, 0x80, 0xff, 0xff, 0xff, 0xff}));
             doReadTest(w, ws, close_code::protocol_error);
         });
 
@@ -322,7 +322,7 @@ public:
         [&](ws_type_t<deflateSupported>& ws)
         {
             put(ws.next_layer().buffer(), cbuf(
-                0x88, 0x02, 0x03, 0xed));
+                {0x88, 0x02, 0x03, 0xed}));
             doFailTest(w, ws, error::bad_close_code);
         });
 
@@ -332,8 +332,8 @@ public:
         {
             w.write_some(ws, false, sbuf("*"));
             w.write_raw(ws, cbuf(
-                0x80, 0xff, 0xff, 0xff, 0xff, 0xff,
-                0xff, 0xff, 0xff, 0xff, 0xff, 0xff, 0xff, 0xff));
+                {0x80, 0xff, 0xff, 0xff, 0xff, 0xff,
+                0xff, 0xff, 0xff, 0xff, 0xff, 0xff, 0xff, 0xff}));
             doReadTest(w, ws, close_code::too_big);
         });
 
@@ -351,7 +351,7 @@ public:
         [&](ws_type_t<deflateSupported>& ws)
         {
             put(ws.next_layer().buffer(), cbuf(
-                0x81, 0x06, 0x03, 0xea, 0xf0, 0x28, 0x8c, 0xbc));
+                {0x81, 0x06, 0x03, 0xea, 0xf0, 0x28, 0x8c, 0xbc}));
             doFailTest(w, ws, error::bad_frame_payload);
         });