[inspector] fixed injected-script-host crash

src/inspector/injected-script-source.js

Index: src/inspector/injected-script-source.js
diff --git a/src/inspector/injected-script-source.js b/src/inspector/injected-script-source.js
index 3a3521a074cf2208316be2697d65a31adbf0da0f..de00422e2a0181553ab94a64eda21ca12a1c3da6 100644
--- a/src/inspector/injected-script-source.js
+++ b/src/inspector/injected-script-source.js
@@ -403,7 +403,9 @@ InjectedScript.prototype = {
                 var descriptor;
                 try {
                     descriptor = InjectedScriptHost.getOwnPropertyDescriptor(o, property);
-                    InjectedScriptHost.nullifyPrototype(descriptor);
+                    if (descriptor) {
+                        InjectedScriptHost.nullifyPrototype(descriptor);
+                    }
                     var isAccessorProperty = descriptor && ("get" in descriptor || "set" in descriptor);
                     if (accessorPropertiesOnly && !isAccessorProperty)
                         continue;