Any of the individual path commands may cause the cr to enter an
error state, for example, if they come with coordinates outside of Cairo's supported range.

The *next* call to the cr will probably be something that actually
checks the status (i.e. in cairo-rs), and we don't want to panic
there.

(In the worst case, Cairo will throw out-of-memory with a super-long
path, but this is the correct place to catch that.)