Fixed small issue in GET /crosschain/trades and GET /crosschain/tradeoffers APIs where 0 was being treated as zero instead of unlimited.

In 2.1.1, unlimited results can be requested by removing the `limit` query string parameter completely, e.g:

http://127.0.0.1:12391/crosschain/trades?foreignBlockchain=LITECOIN&minimumTimestamp=1638835200000&reverse=false

src/main/java/org/qortal/api/resource/CrossChainResource.java

@@ -118,7 +118,7 @@ public class CrossChainResource {
 				crossChainTrades.sort((a, b) -> Longs.compare(a.creationTimestamp, b.creationTimestamp));
 			}
 
-			if (limit != null) {
+			if (limit != null && limit > 0) {
 				// Make sure to not return more than the limit
 				int upperLimit = Math.min(limit, crossChainTrades.size());
 				crossChainTrades = crossChainTrades.subList(0, upperLimit);
@@ -257,7 +257,7 @@ public class CrossChainResource {
 				crossChainTrades.sort((a, b) -> Longs.compare(a.getTradeTimestamp(), b.getTradeTimestamp()));
 			}
 
-			if (limit != null) {
+			if (limit != null && limit > 0) {
 				// Make sure to not return more than the limit
 				int upperLimit = Math.min(limit, crossChainTrades.size());
 				crossChainTrades = crossChainTrades.subList(0, upperLimit);