fix(protocol-designer): disable load liquid save if no liquid selected

When loading a liquid into labware wells in LiquidPlacementForm, we need to disable 'Save' if the
volume is 0, null, or '', OR the selected liquid is null or ''.

Closes RQA-2728

protocol-designer/src/components/LiquidPlacementForm/LiquidPlacementForm.tsx

@@ -237,7 +237,13 @@ export const LiquidPlacementForm = (): JSX.Element | null => {
           </OutlineButton>
           <DeprecatedPrimaryButton
             type="submit"
-            disabled={volumeErrors != null || volume == null || volume === ''}
+            disabled={
+              volumeErrors != null ||
+              volume == null ||
+              volume === '' ||
+              selectedLiquidId == null ||
+              selectedLiquidId === ''
+            }
           >
             {t('button:save')}
           </DeprecatedPrimaryButton>