validate nft genesis (#447)

* validate nft genesis

* Merge branch 'master' into milad/validate-nft-genesis

* addressed PR comments

x/asset/nft/types/genesis.go

@@ -13,6 +13,30 @@ func DefaultGenesis() *GenesisState {
 
 // Validate performs basic genesis state validation returning an error upon any failure.
 func (gs GenesisState) Validate() error {
+	for _, cd := range gs.ClassDefinitions {
+		if err := cd.Validate(); err != nil {
+			return err
+		}
+	}
+
+	for _, frozen := range gs.FrozenNFTs {
+		if err := frozen.Validate(); err != nil {
+			return err
+		}
+	}
+
+	for _, whitelisted := range gs.WhitelistedNFTAccounts {
+		if err := whitelisted.Validate(); err != nil {
+			return err
+		}
+	}
+
+	for _, burnt := range gs.BurntNFTs {
+		if err := burnt.Validate(); err != nil {
+			return err
+		}
+	}
+
 	return gs.Params.ValidateBasic()
 }