fix: fileutils and utils improvements

[DrKJeff16]

Changes

• fileutils.set_file_path() always receives an argument (it's never been used optionally)
• fileutils.save() returns a boolean instead of true|nil
• Added a warning if fileutils.save() returns false
• return nil --> return. The former is redundant
• Got rid of goto continue in for loops. From experience it's problematic.
• Simplified utils statements

[DrKJeff16]

@NeoSahadeo What's wrong?

[NeoSahadeo]

Merged with cherry-pick b94ed45, I needed to revert a change a4da89c; it was causing LSPs to start when the Toggle Window was opened.