Describe the bug (REQUIRED)
For example we move the "tint" fragment constant to vertex attributes
Default value for tint : 1, 1, 1, 1

If we change the tint with
go.set(sprite, "tint.x", 0) - all values for tint will be 0

If we before that call the
go.set(sprite, "tint", vmath.vector4(1)) - all values will be as expected after set tint.x (0, 1, 1, 1)

Also this example is not working on Defold 1.7.1 Beta (I mean the sprites is not rendered with any params with this custom shader)

To Reproduce (REQUIRED)
Steps to reproduce the behavior:

1. Load example
2. Comment/Uncomment the lines to see the difference

	go.set(sprite, "tint", INIT_TINT)
	go.set(sprite1, "tint", INIT_TINT)
	go.set(sprite2, "tint", INIT_TINT)

Expected behavior (REQUIRED)
I have not to re-set the default values for vertex attribute
The example is not working in 1.7.1 (I mean the sprites is not rendered with any params with this custom shader)

Defold version (REQUIRED):
Reproduced on 1.7.0
Not worked in 1.7.1

Platforms (REQUIRED):
Tested on MacOS

Minimal repro case project (OPTIONAL):
vertex_attributes.zip

Workaround (OPTIONAL):
Set initial value for each sprite with that material

Screenshots (OPTIONAL):
Just screen from 1.7.0 from example: