parsing of double-mul does not catch inputs of incorrect types

[airballking]

@mpomarlan reported an error via e-mail to me. I post this for him, here.

The following yaml parses correctly, even though b is not a valid expression:

- a: {vector-sub: [{vector3: [0, 1, 2]}, {vector3: [3, 4, 5]}]}
- b: {double-mul: [-1.0, a]}

[airballking]

In a simple scenario an exception is thrown during parsing:

{double-mul: [-1, {vector3: [1, 2, 3]}]}

However, in Mihai's controller specification it passes. He just showed me on his computer. Maybe it has something to do with the parsing of controller specs...