snarkjs pot contribute with same file as input and ouput causes issue

[samlaf]

Took me a while to figure out this bug. I was contributing to a phase1 powersoftau file with the following commands:

snarkjs powersoftau new bn128 14 pot14.ptau -v
snarkjs powersoftau contribute pot14.ptau pot14.ptau --name="First contribution"
snarkjs powersoftau beacon pot14.ptau pot14_beacon.ptau 

But realized that the second command (notice input file and output file have same name)

snarkjs powersoftau contribute pot14.ptau pot14.ptau --name="First contribution"

causes the file to probably overwrite parts of itself and results in an error

$$$ snarkjs powersoftau verify pot14.ptau         
[INFO]  snarkJS: Powers Of tau file OK!
[ERROR] snarkJS: tauG1 section. Powers do not match

I guess overwriting previous pot contribution files is not a good idea... but would be nice if this was more newbie proof. Made me lose a lot of time to figure this out. Either making this possible, or causing an error like "input and output files must be different" would be very nice.