`GlobalSearch` renders unnecessarily when not empty

Describe the bug

A clear and concise description of what the bug is.

To Reproduce

Steps to reproduce the behavior:

1. Start NUSMods locally (you can't use nusmods.com as we need a development copy of React).

2. Type something into global search.

3. Begin recording a profile in the React Profiler (Chrome version here).

4. Do something unrelated to global search, e.g. go to http://localhost:8080/contribute and click the Show More button in the Map the School section.

5. Stop the recording.

6. Notice GlobalSearch rendered:
   

7. Reload the page, and record another profile without entering anything into global search. Notice that GlobalSearch did not render and that there were fewer renders:
   

Expected behavior

GlobalSearch should not render unnecessarily.

Additional context

It may be easier to fix this after #3039 is merged, so that we can use the React scheduling profiler to see if there are any unexpected state updates.

No source file or test is named. Start NUSMods locally, enter text in global search, and use the React Profiler while performing an unrelated action such as expanding Map the School; done when GlobalSearch no longer renders unnecessarily during that interaction.