fix(masthead): remove console errors (#4404)

### Related Ticket(s)

#4403 

### Description

remove console errors from overflow navigation work

### Changelog

**New**

- checks if components exist before calling function

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packages/react/src/components/Masthead/HeaderNavContainer.js

@@ -107,13 +107,15 @@ const HeaderNavContainer = ({ children }) => {
           records => {
             records.forEach(record => {
               if (
+                contentLeftRef.current &&
                 record.target.classList.contains(
                   contentLeftRef.current.className
                 )
               ) {
                 caretLeftRef.current.hidden = record.isIntersecting;
               }
               if (
+                contentRightRef.current &&
                 record.target.classList.contains(
                   contentRightRef.current.className
                 )
@@ -152,18 +154,20 @@ const HeaderNavContainer = ({ children }) => {
       if (event.shiftKey) {
         //Focus previous input
         if (
+          document.activeElement.parentElement.previousSibling &&
           document.activeElement.parentElement.previousSibling.offsetLeft +
             position <=
-          buttonSize
+            buttonSize
         ) {
           paginateLeft();
         }
       } else {
         //Focus next input
         if (
+          document.activeElement.parentElement.nextSibling &&
           document.activeElement.parentElement.nextSibling.offsetLeft +
             document.activeElement.parentElement.nextSibling.offsetWidth >=
-          containerRef.current.offsetWidth - buttonSize
+            containerRef.current.offsetWidth - buttonSize
         ) {
           paginateRight();
         }