raw: Fix for single element containers

Single element containers have .data() but not .size(), we can make
these fall back to the non-container span constructor.

Change-Id: I68ff3e4dc714aa95a8f9397dc769a2d2cf0f9332
Signed-off-by: William A. Kennington III <wak@google.com>
diff --git a/test/raw.cpp b/test/raw.cpp
index 79fb2ad..a5d4b00 100644
--- a/test/raw.cpp
+++ b/test/raw.cpp
@@ -231,7 +231,14 @@
 
 TEST_CASE("As Span", "[AsSpan]")
 {
-    uint64_t data = htole64(0xffff0000);
+    struct
+    {
+        uint64_t a;
+        uint64_t* data()
+        {
+            return &a;
+        }
+    } data = {htole64(0xffff0000)};
     auto s = asSpan<uint16_t>(data);
     CHECK(s.size() == 4);
     s[2] = 0xfefe;