fix a deserialization overflow edge case
fix a deserialization overflow edge case

A specially-constructed BlockTransactionsRequest can overflow in
deserialization in a way that is currently harmless.

Github-Pull: #14685
Rebased-From: 6bed4b374daf26233e96fa7863d4324a5bfa99c2

ahmedbodi/vertcoin,vmp32k/litecoin,GroestlCoin/GroestlCoin,GroestlCoin/bitcoin,ahmedbodi/vertcoin,h4x3rotab/BTCGPU,guncoin/guncoin,BTCGPU/BTCGPU,thrasher-/litecoin,thrasher-/litecoin,GroestlCoin/GroestlCoin,gjhiggins/vcoincore,ahmedbodi/vertcoin,vertcoin/vertcoin,qtumproject/qtum,thrasher-/litecoin,lbryio/lbrycrd,vertcoin/vertcoin,vmp32k/litecoin,GroestlCoin/GroestlCoin,h4x3rotab/BTCGPU,GroestlCoin/bitcoin,vmp32k/litecoin,lbryio/lbrycrd,ahmedbodi/vertcoin,lbryio/lbrycrd,thrasher-/litecoin,h4x3rotab/BTCGPU,lbryio/lbrycrd,ahmedbodi/vertcoin,gjhiggins/vcoincore,guncoin/guncoin,GroestlCoin/bitcoin,h4x3rotab/BTCGPU,guncoin/guncoin,gjhiggins/vcoincore,vertcoin/vertcoin,qtumproject/qtum,thrasher-/litecoin,GroestlCoin/bitcoin,gjhiggins/vcoincore,digibyte/digibyte,lbryio/lbrycrd,guncoin/guncoin,digibyte/digibyte,gjhiggins/vcoincore,qtumproject/qtum,digibyte/digibyte,GroestlCoin/GroestlCoin,BTCGPU/BTCGPU,BTCGPU/BTCGPU,qtumproject/qtum,ahmedbodi/vertcoin,qtumproject/qtum,thrasher-/litecoin,qtumproject/qtum,vmp32k/litecoin,GroestlCoin/GroestlCoin,vertcoin/vertcoin,digibyte/digibyte,h4x3rotab/BTCGPU,guncoin/guncoin,vertcoin/vertcoin,digibyte/digibyte,BTCGPU/BTCGPU,GroestlCoin/GroestlCoin,vmp32k/litecoin,digibyte/digibyte,vertcoin/vertcoin,guncoin/guncoin,lbryio/lbrycrd,BTCGPU/BTCGPU,qtumproject/qtum,GroestlCoin/bitcoin,BTCGPU/BTCGPU,GroestlCoin/bitcoin,vmp32k/litecoin,h4x3rotab/BTCGPU,gjhiggins/vcoincore,lbryio/lbrycrd