Fix the impl for `Display`ing zero element in Fp (#806) #8

Job	Run time
List directories for parallelizing tests	4s
Check no_std	35s
Check (stable)	12s
Check Documentation	1m 2s
Check Style	14s
Check (nightly)	1m 12s
Test (stable)	9m 16s
Test (nightly)	18m 0s
Test assembly	8m 36s
Test (mnt4_753/)	22m 8s
Test (cp6_782/)	29m 11s
Test (mnt6_753/)	37m 26s
Test (./secq256k1)	1m 10s
Test (./ed_on_mnt4_753)	3m 46s
Test (./vesta)	1m 7s
Test (./ed_on_cp6_782)	1m 15s
Test (./secp384r1)	1m 24s
Test (./bls12_377)	4m 29s
Test (./ed_on_bls12_381)	1m 17s
Test (./pallas)	1m 6s
Test (./ed_on_bw6_761)	38s
Test (./ed_on_bls12_381_bandersnatch)	1m 1s
Test (./mnt4_298)	4m 5s
Test (./secp256k1)	1m 4s
Test (./bn254)	2m 20s
Test (./bls12_381)	3m 17s
Test (./ed_on_bls12_377)	1m 12s
Test (./bw6_761)	4m 4s
Test (./ed25519)	1m 2s
Test (./ed_on_bn254)	1m 6s
Test (./mnt6_298)	5m 37s
Test (./grumpkin)	1m 7s
Test (./bw6_767)	4m 4s
Test (./ed_on_mnt4_298)	1m 4s
Test (./curve25519)	1m 10s
Test (./secp256r1)	1m 3s
	2h 57m 24s

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