d3dx9: Fix ID3DXConstantTable::GetConstantElement() for structs.

dlls/d3dx9_36/shader.c

@@ -1009,7 +1009,7 @@ static D3DXHANDLE WINAPI ID3DXConstantTableImpl_GetConstantElement(ID3DXConstant
 
     if (c && index < c->desc.Elements)
     {
-        if (c->constants) c = &c->constants[index];
+        if (c->desc.Elements > 1) c = &c->constants[index];
         TRACE("Returning constant %p\n", c);
         return handle_from_constant(c);
     }

dlls/d3dx9_36/tests/shader.c

@@ -1848,6 +1848,12 @@ static void test_get_shader_constant_variables(void)
     element = ID3DXConstantTable_GetConstantByName(ctable, "s_2[0]", "invalid");
     ok(element == NULL, "GetConstantByName failed\n");
 
+    constant = ID3DXConstantTable_GetConstantByName(ctable, NULL, "s_2[0]");
+    ok(constant != NULL, "GetConstantByName failed\n");
+
+    element = ID3DXConstantTable_GetConstantElement(ctable, "s_2[0]", 0);
+    ok(constant == element, "GetConstantByName failed, got %p, expected %p\n", element, constant);
+
     count = ID3DXConstantTable_Release(ctable);
     ok(count == 0, "Release failed, got %u, expected %u\n", count, 0);
 }