changed add ref to from NS_ADDREF to NS_IF_ADDREF

Bug 63329, r=kmcclusk sr=buster

layout/forms/nsListControlFrame.cpp

@@ -1007,7 +1007,7 @@ nsIContent *
 nsListControlFrame::GetOptionFromContent(nsIContent *aContent) 
 {
   nsIContent * content = aContent;
-  NS_ADDREF(content);
+  NS_IF_ADDREF(content);
   while (nsnull != content) {
     if (IsOptionElement(content)) {
       return content;

layout/html/forms/src/nsListControlFrame.cpp

@@ -1007,7 +1007,7 @@ nsIContent *
 nsListControlFrame::GetOptionFromContent(nsIContent *aContent) 
 {
   nsIContent * content = aContent;
-  NS_ADDREF(content);
+  NS_IF_ADDREF(content);
   while (nsnull != content) {
     if (IsOptionElement(content)) {
       return content;