__delete shouldn't segfault for null

Author: wilzbach

src/core/memory.d

@@ -1012,13 +1012,19 @@ void __delete(T)(ref T x) @system
 
     static if (is(T == interface) || is(T == class))
     {
-        GC.free(cast(void*) x);
-        x = null;
+        if (x !is null)
+        {
+            GC.free(cast(void*) x);
+            x = null;
+        }
     }
     else static if (is(T == U2*, U2) || is(T : E2[], E2))
     {
-        GC.free(&x);
-        x = null;
+        if (x !is null)
+        {
+            GC.free(&x);
+            x = null;
+        }
     }
 }
 
@@ -1151,4 +1157,17 @@ unittest
 {
     Object x = null;
     __delete(x);
+
+    struct S { ~this() { } }
+    class C { }
+    interface I { }
+
+    int[] a; __delete(a);
+    S[] as; __delete(as);
+    C c; __delete(c);
+    I i; __delete(i);
+    C* pc = &c; __delete(*pc);
+    I* pi = &i; __delete(*pi);
+    int* pint; __delete(pint);
+    S* ps; __delete(ps);
 }