themes/gitstatus: Fix where it shows extra a space

For example, if $HOME is not a git repository, it should show:

    ~>

But previously it incorrectly showed:

    ~ >

This commit makes it aware of such case, inserting the space
accordingly instead of always adding a space.

themes/gitstatus/fish_prompt.fish

@@ -28,8 +28,13 @@ end
 function fish_prompt
   set -l cyan (set_color cyan)
   set -l normal (set_color normal)
+
   set -l cwd (set_color $fish_color_cwd)(prompt_pwd)
+  set -l git_status (_git_status_symbol)(_git_branch_name)
+
+  if test -n "$git_status"
+    set git_status " $git_status"
+  end
 
-  echo -n (_remote_hostname) \
-          $cwd $cyan(_git_status_symbol)(_git_branch_name)$normal'> '
+  echo -n (_remote_hostname) $cwd$cyan$git_status$normal'> '
 end