fix(receive): guard wallet-address rendering against RangeError on short input

lib/screens/receive/widgets/qr_address_widget.dart

@@ -39,20 +39,20 @@ class QRAddressWidget extends StatelessWidget {
                 TextSpan(
                   children: [
                     TextSpan(
-                      text: subtitle.substring(0, 6),
+                      text: _slice(subtitle, 0, 6),
                       style: const TextStyle(fontWeight: .bold),
                     ),
                     const TextSpan(text: ' '),
                     TextSpan(
-                      text: subtitle.substring(6, 21),
+                      text: _slice(subtitle, 6, 21),
                     ),
                     const TextSpan(text: '\n'),
                     TextSpan(
-                      text: subtitle.substring(21, 36),
+                      text: _slice(subtitle, 21, 36),
                     ),
                     const TextSpan(text: ' '),
                     TextSpan(
-                      text: subtitle.substring(36),
+                      text: _slice(subtitle, 36),
                       style: const TextStyle(fontWeight: .bold),
                     ),
                   ],
@@ -72,4 +72,14 @@ class QRAddressWidget extends StatelessWidget {
   );
 
   Future<void> _copyToClipboard() => Clipboard.setData(ClipboardData(text: subtitle));
+
+  // Length-safe slice: a full 0x-address is grouped into fixed chunks, but a
+  // short or empty address must not crash with a RangeError (issue #657 P6 —
+  // this widget renders on both Receive and Settings). Clamps the bounds to
+  // the string length instead of slicing past the end.
+  static String _slice(String value, int start, [int? end]) {
+    if (start >= value.length) return '';
+    final clampedEnd = end == null || end > value.length ? value.length : end;
+    return value.substring(start, clampedEnd);
+  }
 }

test/screens/receive/widgets/qr_address_widget_test.dart

@@ -47,5 +47,24 @@ void main() {
       await tester.tap(find.byType(InkWell));
       await tester.pump();
     });
+
+    testWidgets(
+        'renders a short/unexpected address without a RangeError '
+        '(issue #657 P6 regression)', (tester) async {
+      // A too-short subtitle used to crash on the fixed-index substring(6, 21)
+      // etc. — it must now render gracefully on Receive and Settings.
+      await tester.pumpWidget(_host(
+        const QRAddressWidget(uri: '', subtitle: '0x1234'),
+      ));
+
+      expect(tester.takeException(), isNull);
+      expect(find.textContaining('0x1234'), findsAtLeastNWidgets(1));
+
+      // The extreme case: an empty address must also not throw.
+      await tester.pumpWidget(_host(
+        const QRAddressWidget(uri: '', subtitle: ''),
+      ));
+      expect(tester.takeException(), isNull);
+    });
   });
 }