Fix formatting when no project is loaded

[godric-cz]

When no project is loaded (for example when editing single file by subl --new-window somefile), then plugin fails with stacktrace:

PHP CS Fixer: Formatting view...
PHP CS Fixer: Using config: /home/godric/.php-cs-fixer.php
Traceback (most recent call last):
  File "/opt/sublime_text/Lib/python33/sublime_plugin.py", line 1494, in run_
    return self.run(edit)
  File "/home/godric/.config/sublime-text-3/Installed Packages/PHP CS Fixer.sublime-package/SublimePhpCsFixer.py", line 315, in run
  File "/home/godric/.config/sublime-text-3/Installed Packages/PHP CS Fixer.sublime-package/SublimePhpCsFixer.py", line 329, in format
  File "/home/godric/.config/sublime-text-3/Installed Packages/PHP CS Fixer.sublime-package/SublimePhpCsFixer.py", line 264, in format
  File "/home/godric/.config/sublime-text-3/Installed Packages/PHP CS Fixer.sublime-package/SublimePhpCsFixer.py", line 288, in format_contents
  File "/home/godric/.config/sublime-text-3/Installed Packages/PHP CS Fixer.sublime-package/SublimePhpCsFixer.py", line 300, in format_file
  File "/home/godric/.config/sublime-text-3/Installed Packages/PHP CS Fixer.sublime-package/SublimePhpCsFixer.py", line 162, in run
  File "/home/godric/.config/sublime-text-3/Installed Packages/PHP CS Fixer.sublime-package/SublimePhpCsFixer.py", line 184, in create_cmd
  File "/home/godric/.config/sublime-text-3/Installed Packages/PHP CS Fixer.sublime-package/SublimePhpCsFixer.py", line 234, in get_configured_php_cs_fixer_path
  File "/home/godric/.config/sublime-text-3/Installed Packages/PHP CS Fixer.sublime-package/SublimePhpCsFixer.py", line 246, in locate_php_cs_fixer
  File "/home/godric/.config/sublime-text-3/Installed Packages/PHP CS Fixer.sublime-package/SublimePhpCsFixer.py", line 55, in fixer_possible_paths
TypeError: 'NoneType' object is not subscriptable

This handles the situation and tries to load <project>/vendor/bin/php-cs-fixer only when project is not None.

[adael]

Thanks you for your PR!