Fix uninitialized variable compiler errors [GCC 4.8.4]

src/runtime/runtime-scopes.cc

Index: src/runtime/runtime-scopes.cc
diff --git a/src/runtime/runtime-scopes.cc b/src/runtime/runtime-scopes.cc
index 8dedcea6b0418866544c6beceab576e9f3ebe164..7bc24afbcb489ca4ccdae4cddd20d458ef786796 100644
--- a/src/runtime/runtime-scopes.cc
+++ b/src/runtime/runtime-scopes.cc
@@ -1063,7 +1063,7 @@ RUNTIME_FUNCTION(Runtime_GetArgumentsProperty) {
 
   // Try to convert the key to an index. If successful and within
   // index return the the argument from the frame.
-  uint32_t index;
+  uint32_t index = 0;
   if (raw_key->ToArrayIndex(&index) && index < n) {
     return frame->GetParameter(index);
   }