fix: added input validation

Author: samruddhi-Rahegaonkar

lib/badge_animation/ani_snowflake.dart

@@ -9,9 +9,21 @@ class SnowFlakeAnimation extends BadgeAnimation {
     List<List<bool>> processGrid,
     List<List<bool>> canvas,
   ) {
+    if (processGrid.isEmpty ||
+        processGrid.any((row) => row.length != processGrid[0].length)) {
+      throw ArgumentError(
+        'processGrid must be a non-empty rectangular 2D list',
+      );
+    }
     int newGridHeight = processGrid.length;
     int newGridWidth = processGrid[0].length;
 
+    if (canvas.length < badgeHeight ||
+        canvas.any((row) => row.length < badgeWidth)) {
+      throw ArgumentError(
+        'canvas must have at least $badgeHeight rows and $badgeWidth columns',
+      );
+    }
     int framesCount = (newGridWidth / badgeWidth).ceil();
     framesCount = framesCount == 0 ? 1 : framesCount;