Fix minify-whitespace case undefined

[krk]

Print a space before undefined in printUndefined.

fix #6750

What does this PR do?

Fix minify-whitespace formatting error.

How did you verify your code works?

I wrote automated tests

• I checked the lifetime of memory allocated to verify it's (1) freed and (2) only freed when it should be
• I or my editor ran zig fmt on the changed files
• I included a test for the new code, or an existing test covers it
• JSValue used outside outside of the stack is either wrapped in a JSC.Strong or is JSValueProtect'ed

[dylan-conway]

Thank you