Fix crash in PanelSyncHandler and TextFieldHandler (#133)

Co-authored-by: brachy <45517902+brachy84@users.noreply.github.com>

Author: Luca-Guettinger

src/main/java/com/cleanroommc/modularui/value/sync/PanelSyncHandler.java

@@ -112,8 +112,11 @@ public void closeSubPanels() {
     @ApiStatus.Internal
     @Override
     public void closePanelInternal() {
-        getSyncManager().getModularSyncManager().close(this.panelName);
         this.open = false;
+        // Sync infrastructure may already be torn down if the screen was disposed
+        // (e.g. deferred PanelManager.dispose() running after ModularNetwork.closeAll())
+        if (!isValid()) return;
+        getSyncManager().getModularSyncManager().close(this.panelName);
         if (getSyncManager().isClient()) {
             syncToServer(SYNC_CLOSE);
         }

src/main/java/com/cleanroommc/modularui/widgets/textfield/TextFieldHandler.java

@@ -327,8 +327,10 @@ private Point insert(List<String> text, List<String> insertion) {
             text.addAll(insertion);
             return new Point(text.get(text.size() - 1).length(), text.size() - 1);
         }
-        String lineStart = text.get(this.cursor.y).substring(0, this.cursor.x);
-        String lineEnd = text.get(this.cursor.y).substring(this.cursor.x);
+        String line = text.get(this.cursor.y);
+        int cursorX = Math.min(this.cursor.x, line.length());
+        String lineStart = line.substring(0, cursorX);
+        String lineEnd = line.substring(cursorX);
         if (insertion.size() == 1 && text.size() == 1 && !test(lineStart + insertion.get(0) + lineEnd)) {
             return null;
         }
@@ -338,7 +340,7 @@ private Point insert(List<String> text, List<String> insertion) {
                 return null;
             }
             text.set(this.cursor.y, text.get(this.cursor.y) + lineEnd);
-            return new Point(this.cursor.x + insertion.get(0).length(), this.cursor.y);
+            return new Point(cursorX + insertion.get(0).length(), this.cursor.y);
         } else {
             text.add(this.cursor.y + 1, insertion.get(insertion.size() - 1) + lineEnd);
             x = insertion.get(insertion.size() - 1).length();