fix Issue 6217 - [GSOC] result of std.algorithm.map is not movable

It's so simple, and it's been ages as it was broken.

std/algorithm.d

@@ -1406,7 +1406,7 @@ unittest
 /// Ditto
 T move(T)(ref T src)
 {
-    T result;
+    T result=void;
     move(src, result);
     return result;
 }
@@ -8724,3 +8724,9 @@ unittest
     //writeln(b[0]);
     assert(b[0] == tuple(4.0, 2u));
 }
+
+unittest//Issue 6217 
+{
+    auto x = map!"a"([1,2,3]);
+    x = move(x);
+}