[rebber-plugins]Escapement issue with command inside command

[artragis]

When using rebber with rebber-plugin, especially the math plugin, we have issues with escaping

Input

$$\Delta \varphi = 2 \pi f \Delta t_{orange/bleu} = -\frac{\pi}{4}$$

Actual Output

$$\Delta \varphi = 2 \pi f \Delta t_{orange/bleu} = -\frac{ {4}}$$

Expected output

$$\Delta \varphi = 2 \pi f \Delta t_{orange/bleu} = -\frac{\pi}{4}$$

Note : the issue is also present in the full display version of math.

The \frac{\pi}{4} is transformed into \frac{{4}}