Unary negation does not work correctly when using CONST

[a740g]

Describe the bug
Unary negation does not work correctly when using CONST. As @mkilgore figured out, the unary negation only works correctly for integers. See here.

To Reproduce

CONST C1! = -1.4!
CONST C2! = -0.4!
CONST C3! = 0.4!
CONST C4! = 1.4!

PRINT C1, C2, C3, C4

The above code prints: -1 0 .4 1.4

Expected behavior
It should handle unary negation correctly for both integer and floating-point values.

Additional context
This was first reported here.