common-aliases: check if `$XIVIEWER` is defined and minor fixes

plugins/common-aliases/common-aliases.plugin.zsh

@@ -55,15 +55,17 @@ alias mv='mv -i'
 if is-at-least 4.2.0; then
   # open browser on urls
   if [[ -n "$BROWSER" ]]; then
-    _browser_fts=(htm html de org net com at cx nl se dk dk)
+    _browser_fts=(htm html de org net com at cx nl se dk)
     for ft in $_browser_fts; do alias -s $ft=$BROWSER; done
   fi
 
   _editor_fts=(cpp cxx cc c hh h inl asc txt TXT tex)
   for ft in $_editor_fts; do alias -s $ft=$EDITOR; done
 
-  _image_fts=(jpg jpeg png gif mng tiff tif xpm)
-  for ft in $_image_fts; do alias -s $ft=$XIVIEWER; done
+  if [[ -n "$XIVIEWER" ]]; then
+    _image_fts=(jpg jpeg png gif mng tiff tif xpm)
+    for ft in $_image_fts; do alias -s $ft=$XIVIEWER; done
+  fi
 
   _media_fts=(ape avi flv m4a mkv mov mp3 mpeg mpg ogg ogm rm wav webm)
   for ft in $_media_fts; do alias -s $ft=mplayer; done
@@ -85,4 +87,3 @@ fi
 
 # Make zsh know about hosts already accessed by SSH
 zstyle -e ':completion:*:(ssh|scp|sftp|rsh|rsync):hosts' hosts 'reply=(${=${${(f)"$(cat {/etc/ssh_,~/.ssh/known_}hosts(|2)(N) /dev/null)"}%%[# ]*}//,/ })'
-