Variance of a variable from a wedge-shaped joint density

Let $\underline X=(X_1,X_2)$ have joint probability density function

$$f(x_1,x_2)=\begin{cases}\dfrac{e^{-x_2^2/2}}{x_2\sqrt{2\pi}}, & 0<|x_1|\le x_2<\infty,\ 0, & \text{otherwise.}\end{cases}$$

Then the variance of random variable $X_1$ is