Uniforms in shaderGraph shader doesn't show until editor is restarted.

[henkz1]

Operating system or device - Godot version: Ubuntu 16.04, master https://github.com/godotengine/godot/commit/a0dd7ec171001f9b9a14bafc0c9ed12623908984

Issue description (what happened, and what was expected): Adding a uniform to shaderGraph it won't show in the inspector until editor is restarted.

Steps to reproduce:

• create a shaderGraph shader
• add a texture uniform(or any uniform)
• navigate back to the material, you won't find any param for the uniform until you restart godot

Link to minimal example project (optional but very welcome):

[reduz]

@MarianoGnu