fix nil pointer, see 1198

[jordipainan]

closes #1198

[p4u]

Please check this same issue does not happend on other handlers.

[coveralls]

Pull Request Test Coverage Report for Build 6972357204

• 14 of 35 (40.0%) changed or added relevant lines in 3 files are covered.
• 2 unchanged lines in 1 file lost coverage.
• Overall coverage increased (+0.1%) to 61.764%

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Changes Missing Coverage	Covered Lines	Changed/Added Lines	%
vochain/transaction/vochaintx/vochaintx.go	5	9	55.56%
api/accounts.go	5	11	45.45%
vochain/cometbft.go	4	15	26.67%

Files with Coverage Reduction	New Missed Lines	%
data/ipfs/ipfs.go	2	54.64%

Totals
Change from base Build 6944527117:	0.1%
Covered Lines:	14661
Relevant Lines:	23737

---

💛 - Coveralls

[p4u]

Btw, the issue seems to be at

go.vocdoni.io/dvote/vochain/transaction/vochaintx.(*Tx).Unmarshal(0xc01c6335e0, {0x0, 0x0, 0x0}, {0xc002930060, 0xe})
	go.vocdoni.io/dvote/vochain/transaction/vochaintx/vochaintx.go:39 +0x20d
go.vocdoni.io/dvote/vochain.(*BaseApplication).CheckTx(0xc0044d6420, {0x40?, 0x36c0a00?}, 0xc01c62c4a0)
	go.vocdoni.io/dvote/vochain/cometbft.go:196 +0x44a

So the check must exist in the API layer but also on the vochain transaction handler.

[jordipainan]

Btw, the issue seems to be at

go.vocdoni.io/dvote/vochain/transaction/vochaintx.(*Tx).Unmarshal(0xc01c6335e0, {0x0, 0x0, 0x0}, {0xc002930060, 0xe})
	go.vocdoni.io/dvote/vochain/transaction/vochaintx/vochaintx.go:39 +0x20d
go.vocdoni.io/dvote/vochain.(*BaseApplication).CheckTx(0xc0044d6420, {0x40?, 0x36c0a00?}, 0xc01c62c4a0)
	go.vocdoni.io/dvote/vochain/cometbft.go:196 +0x44a

So the check must exist in the API layer but also on the vochain transaction handler.

added extra checks on comet and to the tx unmarshaling content