Fix error on SendFeedback page (fixes #2951)

If some piece of information isn't available on a particular
system (in my case, vram), then `systeminformation` produces a
`null` value when queried. `null` satisfies the `typeof === 'object`'
check, causing us to attempt to iterate over it, even though it's
not iterable.

Excluding `null` from such attempts keeps the SendFeedback page
from crashing.

src/renderer/modal-widgets/SendFeedback.tsx

@@ -481,7 +481,7 @@ ${log}
       );
     }
 
-    if (typeof input === "object") {
+    if (typeof input === "object" && input !== null) {
       return (
         <>
           {Object.keys(input).map((k) => (