[Search git status] Fix previewing paths with spaces

Previously, paths containing spaces broke the preview. Turns out the
qutoes added by git status for paths containing spaces were being passed
literally to git diff as part of the path and thus git diff could not
find the file.

functions/_fzf_preview_changed_file.fish

@@ -4,7 +4,10 @@
 #  D README.md
 # R  LICENSE.md -> LICENSE
 function _fzf_preview_changed_file --description "Show the untracked, staged, and/or unstaged changes in the given file."
-    set -l path (string split ' ' $argv)[-1]
+    # remove quotes because they'll be interpreted literally by git diff
+    # don't requote when referencing $path because fish does not perform word splitting
+    # https://fishshell.com/docs/current/fish_for_bash_users.html
+    set -l path (string unescape (string sub --start 4 $argv))
     # first letter of short format shows index, second letter shows working tree
     # https://git-scm.com/docs/git-status/2.35.0#_output
     set -l index_status (string sub --length 1 $argv)

tests/preview_changed_file/path_with_spaces.fish

@@ -0,0 +1,9 @@
+set path_with_space "tests/_resources/multi word dir/file 1.txt"
+set expected_diff a-very-unique-line
+echo $expected_diff >>$path_with_space
+set output (_fzf_preview_changed_file " M \"$path_with_space\"")
+
+string match --entire --quiet $expected_diff $output
+@test "git diff successfully invoked on path with space" $status -eq 0
+
+git restore $path_with_space