Real (ID value of the shader, or -1 if no shader)
This function will return the index ID value of the shader currently being used for rendering, or it will return -1 if no shader is being used.IMPORTANT! This function is not available with the Trial Licence of the product.
if shader_current() == -1
The above code will check to see what the current shader is and if it returns -1 (no shader being used) then a shader is set.