allocator_traits::construct is used for user-defined types:

It should only be called when constructing a user-provided type.

Close #1332

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

test/beast/core/buffers_cat.cpp

@@ -302,6 +302,21 @@ public:
             buffers_cat(buffers_prefix(i, buffers), cb));
     }
 
+    void
+    testSingleBuffer()
+    {
+        char c[1] = {};
+        auto b = net::const_buffer(c, 1);
+        auto bs = buffers_cat(net::const_buffer(c, 1));
+        auto first = net::buffer_sequence_begin(bs);
+        auto last = net::buffer_sequence_end(bs);
+        BOOST_ASSERT(first != last);
+        BEAST_EXPECT(std::distance(first, last) == 1);
+        net::const_buffer b2(*first);
+        BEAST_EXPECT(b.data() == b2.data());
+        BEAST_EXPECT(b.size() == b2.size());
+    }
+
     void run() override
     {
         testBufferSequence();
@@ -309,6 +324,7 @@ public:
         testEmpty();
         testGccWarning1();
         testGccWarning2();
+        testSingleBuffer();
     }
 };