Throw multi pages error explicitly (#1455)

 # Changelog
 
+## 3.10.6
+
+- Throw multi page error explicitly.
+
 ## 3.10.5
 
 - Improve TTF writer with multi-compound characters

@@ -246,14 +246,11 @@ class MultiPage extends Page {
     while (_index < children.length) {
       final child = children[_index];
 
-      assert(() {
-        // Detect too big widgets
-        if (sameCount++ > maxPages) {
-          throw Exception(
-              'This widget created more than $maxPages pages. This may be an issue in the widget or the document. See https://pub.dev/documentation/pdf/latest/widgets/MultiPage-class.html');
-        }
-        return true;
-      }());
+      // Detect too big widgets
+      if (sameCount++ > maxPages) {
+        throw TooManyPagesException(
+            'This widget created more than $maxPages pages. This may be an issue in the widget or the document. See https://pub.dev/documentation/pdf/latest/widgets/MultiPage-class.html');
+      }
 
       // Create a new page if we don't already have one
       if (context == null || child is NewPage) {
@@ -579,3 +576,10 @@ class MultiPage extends Page {
     }
   }
 }
+
+/// Exception thrown when generator populates more pages than [maxPages].
+class TooManyPagesException implements Exception {
+  TooManyPagesException(this.message);
+
+  final String message;
+}

@@ -6,7 +6,7 @@ issue_tracker: https://github.com/DavBfr/dart_pdf/issues
 screenshots:
   - description: 'Example of a generated document'
     path: example.jpg
-version: 3.10.5
+version: 3.10.6
 
 environment:
   sdk: ">=2.18.0 <4.0.0"