Fix Rect.fromLTRB zero-dimension errors causing rendering crashes

lib/drawing/harmony_beat_renderer.dart

@@ -163,7 +163,7 @@ class HarmonyBeatRenderer {
 
     canvas.drawRect(
         Rect.fromLTRB(bounds.left + leftOffset, bounds.top,
-            bounds.left + leftOffset, bounds.bottom),
+            bounds.left + leftOffset + 1, bounds.bottom),
         paint);
     canvas.drawRect(
         Rect.fromLTRB(bounds.right - rightOffset, bounds.top, bounds.right,

lib/music_view/music_system_painter.dart

@@ -263,7 +263,7 @@ class MusicSystemPainter extends CustomPainter {
           }
 //        print("fontSize=$fontSize topOffset=$topOffset");
           double opacityFactor =
-              magicOpacityFactor(Rect.fromLTRB(left, 0, left, 0));
+              magicOpacityFactor(Rect.fromLTRB(left, 0, left + 1, 1));
           TextSpan span = TextSpan(
               text: renderingSection.canonicalName,
               style: TextStyle(

test/music_system_painter_test.dart

@@ -0,0 +1,61 @@
+import 'package:flutter/material.dart';
+import 'package:flutter_test/flutter_test.dart';
+
+void main() {
+  group('Rect.fromLTRB fix', () {
+    test('Fixed rectangle creation should have valid dimensions', () {
+      // Test the specific fix for the zero-dimension rectangle issue
+      const double left = 50.0;
+
+      // This is the NEW fixed way that prevents zero dimensions
+      final fixedRect = Rect.fromLTRB(left, 0, left + 1, 1);
+
+      // Verify the rectangle has valid dimensions
+      expect(fixedRect.width, equals(1.0));
+      expect(fixedRect.height, equals(1.0));
+      expect(fixedRect.left, equals(left));
+      expect(fixedRect.top, equals(0.0));
+      expect(fixedRect.right, equals(left + 1));
+      expect(fixedRect.bottom, equals(1.0));
+
+      // Ensure it's not empty
+      expect(fixedRect.isEmpty, isFalse);
+    });
+
+    test('Zero dimension rectangles should be avoided', () {
+      // Demonstrate the problem that was fixed
+      const double left = 50.0;
+
+      // The old problematic way
+      final oldRect = Rect.fromLTRB(left, 0, left, 0);
+      expect(oldRect.width, equals(0.0));
+      expect(oldRect.height, equals(0.0));
+      expect(oldRect.isEmpty, isTrue);
+
+      // The new fixed way
+      final newRect = Rect.fromLTRB(left, 0, left + 1, 1);
+      expect(newRect.width, equals(1.0));
+      expect(newRect.height, equals(1.0));
+      expect(newRect.isEmpty, isFalse);
+    });
+
+    test('Zero-width rectangles for vertical lines should have minimal width', () {
+      // Test the harmony beat renderer fix
+      final bounds = Rect.fromLTRB(0, 0, 100, 50);
+      const double leftOffset = 10.0;
+
+      // This was the old problematic way (zero width)
+      final oldRect = Rect.fromLTRB(bounds.left + leftOffset, bounds.top,
+          bounds.left + leftOffset, bounds.bottom);
+      expect(oldRect.width, equals(0.0));
+      expect(oldRect.isEmpty, isTrue);
+
+      // This is the new fixed way (minimal 1px width)
+      final newRect = Rect.fromLTRB(bounds.left + leftOffset, bounds.top,
+          bounds.left + leftOffset + 1, bounds.bottom);
+      expect(newRect.width, equals(1.0));
+      expect(newRect.height, equals(bounds.height));
+      expect(newRect.isEmpty, isFalse);
+    });
+  });
+}