[BUG] Global install fails if prefix directory doesn't exist

[t1m0thyj]

Current Behavior:

In NPM 7.x, npm install fails when both the --global and --prefix flags are set.

Expected Behavior:

Same as NPM 6.x: The prefix directory should be created if it doesn't exist and the global install should succeed.

Steps To Reproduce:

1. Use NPM 7.x (this works fine with NPM 6.x)
2. Run npm install typescript -g --prefix <nonExistentDir>
   • change "<nonExistentDir>" to a path that doesn't exist
   • the package name being installed doesn't matter
3. See error ENOENT: no such file or directory, lstat '<nonExistentDir>'
4. Create "<nonExistentDir>" manually
5. Repeat the command from step 2
6. Still see error ENOENT: no such file or directory, lstat '<nonExistentDir>/lib'

Environment:

• OS: Ubuntu 18.04
• Node: 15.3.0
• npm: 7.0.15