Support identical minPort and maxPort in SocketUtils (#1612)

This commit fixes a bug where an IllegalStateException was
thrown if the minPort and maxPort values supplied to
SocketUtils.findAvailableTcpPort(int, int) were identical.

spring-core/src/main/java/org/springframework/util/SocketUtils.java

@@ -258,7 +258,7 @@ public class SocketUtils {
 			int candidatePort;
 			int searchCounter = 0;
 			do {
-				if (++searchCounter > portRange) {
+				if (searchCounter++ > portRange) {
 					throw new IllegalStateException(String.format(
 							"Could not find an available %s port in the range [%d, %d] after %d attempts",
 							name(), minPort, maxPort, searchCounter));