Simplify some code

See gh-17837

spring-boot-project/spring-boot-devtools/src/main/java/org/springframework/boot/devtools/filewatch/FileSystemWatcher.java

@@ -154,8 +154,7 @@ public class FileSystemWatcher {
 		synchronized (this.monitor) {
 			saveInitialSnapshots();
 			if (this.watchThread == null) {
-				Map<File, FolderSnapshot> localFolders = new HashMap<>();
+				Map<File, FolderSnapshot> localFolders = new HashMap<>(this.folders);
-				localFolders.putAll(this.folders);
 				this.watchThread = new Thread(new Watcher(this.remainingScans, new ArrayList<>(this.listeners),
 						this.triggerFilter, this.pollInterval, this.quietPeriod, localFolders));
 				this.watchThread.setName("File Watcher");