Fix branch preview for branches that have the same name as a file

[sandr01d]

Check list

• I have performed a self-review of my code
• I have commented my code in hard-to-understand areas
• I have made corresponding changes to the documentation

Description

The preview for branches (when using gbd or gcb) did not work for branches that have the same name as a file in the repository.
The preview creates the following error message when adding a branch called 'LICENSE' to this repository and trying to preview it:

fatal: ambiguous argument 'LICENSE': both revision and filename                                                                                     

Use '--' to separate paths from revisions, like this:                                                                                               

'git <command> [<revision>...] -- [<file>...]'

This PR fixes this behavior by separating files and revisions with '--' as git suggests, while leaving the files blank to keep matching all files.

Type of change

• Bug fix
• New feature
• Refactor
• Breaking change
• Documentation change

Test environment

• Shell
  • bash
  • zsh
  • fish
• OS
  • Linux
  • Mac OS X
  • Windows
  • Others:

[carlfriedrich]

Good catch! Can reproduce the error, and the fix works for me. Thanks!