Fix short jump address calculation in x64 disassembler

runtime/observatory/lib/src/service/object.dart

Index: runtime/observatory/lib/src/service/object.dart
diff --git a/runtime/observatory/lib/src/service/object.dart b/runtime/observatory/lib/src/service/object.dart
index 1c6fc0f68b0e326851d3bc2144851b5cd9e2200f..9d479c785053d8fb58a61bad555f8a64469478ed 100644
--- a/runtime/observatory/lib/src/service/object.dart
+++ b/runtime/observatory/lib/src/service/object.dart
@@ -3149,8 +3149,14 @@ class CodeInstruction extends Observable {
     if (address == 0) {
       return;
     }
-
-    jumpTarget = instructionsByAddressOffset[address - startAddress];
+    var relativeAddress = address - startAddress;
+    if (relativeAddress < 0) {
+      return;
+    }
+    if (relativeAddress >= instructionsByAddressOffset.length) {
+      return;
+    }

[srdjan, 2015/08/11 06:17:45]

You may want to report it to console that there is an issue with
relativeAddress.

[Cutch, 2015/08/11 13:17:04]

Done.

+    jumpTarget = instructionsByAddressOffset[relativeAddress];
   }
 }