Use InsnList's iterator instead of getFirst()/getNext()

asm/src/main/java/dev/openrs2/asm/InsnMatcher.java

@@ -216,7 +216,8 @@ public final class InsnMatcher {
 
 	private static List<AbstractInsnNode> createRealInsnList(InsnList list) {
 		List<AbstractInsnNode> realInsns = new ArrayList<>();
-		for (var insn = list.getFirst(); insn != null; insn = insn.getNext()) {
+		for (var it = list.iterator(); it.hasNext(); ) {
+			var insn = it.next();
 			if (insn.getOpcode() != -1) {
 				realInsns.add(insn);
 			}

deob/src/main/java/dev/openrs2/deob/transform/CounterTransformer.java

@@ -47,7 +47,8 @@ public final class CounterTransformer extends Transformer {
 	}
 
 	private void findCounters(MethodNode method, Map<MemberRef, Integer> references, Map<MemberRef, Integer> resets, Map<MemberRef, Integer> increments) {
-		for (var insn = method.instructions.getFirst(); insn != null; insn = insn.getNext()) {
+		for (var it = method.instructions.iterator(); it.hasNext(); ) {
+			var insn = it.next();
 			if (insn.getType() != AbstractInsnNode.FIELD_INSN) {
 				continue;
 			}

deob/src/main/java/dev/openrs2/deob/transform/FieldOrderTransformer.java

@@ -20,7 +20,8 @@ public final class FieldOrderTransformer extends Transformer {
 				var fields = new HashMap<MemberDesc, Integer>();
 				var index = 0;
 
-				for (var insn = ctor.instructions.getFirst(); insn != null; insn = insn.getNext()) {
+				for (var it = ctor.instructions.iterator(); it.hasNext(); ) {
+					var insn = it.next();
 					if (insn.getOpcode() != opcode) {
 						continue;
 					}