chore(comment): Add code comments

Author: BigtoC

x/wasm/keeper/query_plugins.go

@@ -827,6 +827,7 @@ func ConvertSdkDenomUnitsToWasmDenomUnits(denomUnits []*banktypes.DenomUnit) []w
 			Exponent: u.Exponent,
 			Aliases:  u.Aliases,
 		}
+		// Return nil may break cosmwasm-std
 		if u.Aliases == nil {
 			converted[i].Aliases = []string{}
 		}