fix(tx): return short transaction ids whole instead of a RangeError

lib/packages/service/transaction_history_service.dart

@@ -129,6 +129,10 @@ extension ToEpiAddress on String {
   String get asHexEip55 => EthereumAddress.fromHex(this).hexEip55;
 
   String get asShortTxId {
+    // A txid shorter than the elided form (10 + "..." + 10 = 23) is returned
+    // whole: slicing it would throw a RangeError for length < 10 and overlap
+    // the head/tail for length < 20 (issue #657 P9 L1).
+    if (length <= 23) return this;
     return '${substring(0, 10)}...${substring(length - 10)}';
   }
 }

test/packages/service/transaction_history_service_test.dart

@@ -177,5 +177,15 @@ void main() {
       expect(txid.asShortTxId.contains('...'), isTrue);
       expect(txid.asShortTxId.length, 23); // 10 + 3 + 10
     });
+
+    test('asShortTxId returns a short id whole without a RangeError '
+        '(issue #657 P9 L1 regression)', () {
+      // Anything not longer than the elided form is shown whole; the old code
+      // crashed with a RangeError on substring(0, 10) / substring(length - 10)
+      // for these inputs.
+      expect('0xabc'.asShortTxId, '0xabc');
+      expect(''.asShortTxId, '');
+      expect('0x12345678'.asShortTxId, '0x12345678'); // length 10, would overlap
+    });
   });
 }