`onefile = FALSE` does not work with **tikzDevice** 0.12.4

Hello,

```r
library(tikzDevice) # 0.12.4
tikz(onefile = FALSE)
plot(0, 0, pch = 19)
plot(0, 0, pch = 19)
dev.off()
```

This creates a file named **Rplot%03d.tex** (I mean the `%03d` is not substitued) which is empty and immediately disappears. Providing a file name does not work too.