qgam() gives error if only parametric terms included in the model

[mfasiolo]

This code gives and error

`x <- rnorm(1e2)
y <- x^2 + rnorm(1e2)
qgam(y~x, qu = 0.5, data = data.frame("x" = x, "y" = y))

Error in if (sum(fix.ind)) { : argument is not interpretable as logical
`

[mfasiolo]

Fixed here 157a77d