Patches with-environment.sh script (facebook#42184)

Summary:
Closes facebook#42164

## Changelog:

[IOS] [FIXED] - Fixes `with-environment.sh` script for the case when Node can't be found prior to loading `.xcode.env`

Pull Request resolved: facebook#42184

Test Plan: This is a trivial update, no need for much testing.

Reviewed By: cortinico

Differential Revision: D52602653

Pulled By: cipolleschi

fbshipit-source-id: 0881456bf165d895252ae38cb7c7aee945cfaf52

packages/react-native/scripts/xcode/with-environment.sh

@@ -13,7 +13,7 @@
 # ./with-environment.sh command
 
 # Start with a default
-NODE_BINARY=$(command -v node)
+NODE_BINARY=$(command -v node || echo "")
 export NODE_BINARY
 
 # Override the default with the global environment