Resolve errors when printing or writing empty TaskLists

data/tasks.txt

@@ -1,3 +0,0 @@
-D | 0 | submit increments | 2020-08-02
-T | 1 | go to school
-E | 0 | festival | 2020-10-09

src/META-INF/MANIFEST.MF

@@ -0,0 +1,3 @@
+Manifest-Version: 1.0
+Main-Class: duke.main.Duke
+

src/java/duke/main/TaskList.java

@@ -66,7 +66,9 @@ String write() {
         for (Task task : tasks) {
             stringBuilder.append(task.print()).append(System.lineSeparator());
         }
-        stringBuilder.deleteCharAt(stringBuilder.length() - 1);
+        if (stringBuilder.length() != 0) {
+            stringBuilder.deleteCharAt(stringBuilder.length() - 1);
+        }
         return stringBuilder.toString();
     }
 
@@ -115,7 +117,9 @@ public String toString() {
                     .append(task)
                     .append(System.lineSeparator());
         }
-        list.deleteCharAt(list.length() - 1);
+        if (list.length() != 0) {
+            list.deleteCharAt(list.length() - 1);
+        }
         return list.toString();
     }
 }