Fix maybe-uninitialized warning in ecma-objects.c

[glistening]

During building jerryscript with arm-gcc-noneeabi 4.9.3,
maybe-uninitialized warning occurred. This patch fixed the warning.

JerryScript-DCO-1.0-Signed-off-by: Sanggyu Lee sg5.lee@samsung.com

[glistening]

When I build jerrryscript for tizenrt on artik05x, I met the following warning:

/home/brian/iotjs/jerry-tizenrt/jerryscript/jerry-core/ecma/operations/ecma-objects.c: In function 'ecma_op_object_put':
/home/brian/iotjs/jerry-tizenrt/jerryscript/jerry-core/ecma/operations/ecma-objects.c:862:20: error: 'property_ref.value_p' may be used uninitialized in this function [-Werror=maybe-uninitialized]
           setter_p = ecma_get_named_accessor_property_setter (property_ref.value_p);

I fixed the warning by explicitly setting NULL for the union variable.
We use gcc-none-eabi 4.9.3.

[LaszloLango]

LGTM

[zherczeg]

LGTM