When asked to remove a property that doesn't exist, don't try too hard (and crash). b=245572 r+sr=bryner

git-svn-id: svn://10.0.0.236/trunk@157526 18797224-902f-48f8-a5cc-f745e15eee43

mozilla/layout/style/nsDOMCSSDeclaration.cpp

@@ -198,6 +198,9 @@ nsDOMCSSDeclaration::RemoveProperty(const nsAString& aPropertyName,
   }
 
   nsCSSProperty prop = nsCSSProps::LookupProperty(aPropertyName);
+  if (prop == eCSSProperty_UNKNOWN) {
+    return NS_OK;
+  }
 
   decl->GetValue(prop, aReturn);