utility: Always use 'git' fallback for 'wdiff' wrapper

Use `git` fallback (if present) even when color is off and `wdiff` is
not present.

Further, remove redundant `function` clause as per Prezto convention.

modules/utility/functions/wdiff

@@ -3,9 +3,11 @@
 #
 # Authors:
 #   Sorin Ionescu <sorin.ionescu@gmail.com>
+#   Indrajit Raychaudhuri <irc@indrajit.com>
 #
 
-function wdiff {
+# function wdiff {
+
 if zstyle -t ':prezto:module:utility:wdiff' color; then
   if (( $+commands[wdiff] )); then
     command wdiff \
@@ -17,13 +19,14 @@ function wdiff {
           "$@" \
       | sed 's/^\(@@\( [+-][[:digit:]]*,[[:digit:]]*\)\{2\} @@\)$/;5;6m\10m/g'
   elif (( $+commands[git] )); then
-      command git --no-pager diff --color=auto --no-ext-diff --no-index --color-words "$@"
+    command git --no-pager diff --no-ext-diff --no-index --color=auto --color-words "$@"
   else
     command wdiff "$@"
   fi
+elif (( ! $+commands[wdiff] && $+commands[git] )); then
+    command git --no-pager diff --no-ext-diff --no-index --color=never "$@"
 else
   command wdiff "$@"
 fi
-}
 
-wdiff "$@"
+# }