Fix Missing SecLoop#nextValue Reset (#7989)

Author: Absolutionism

src/main/java/ch/njol/skript/sections/SecLoop.java

@@ -228,6 +228,7 @@ public void exit(Event event) {
 		current.remove(event);
 		iteratorMap.remove(event);
 		previous.remove(event);
+		nextValue = null;
 		super.exit(event);
 	}
 

src/test/skript/tests/regressions/7989-secloop next value.sk

@@ -0,0 +1,10 @@
+local function loop():
+	loop 4 times:
+		assert previous loop-value is not set with "Previous loop-value should not be set"
+		assert loop-value is 1 with "Current loop-value should be 1"
+		assert next loop-value is 2 with "Next loop-value should be 2"
+		stop
+
+test "secloop next value":
+	loop 4 times:
+		loop()