plugins/less-pretty-cat: use `_command_exists`

Addresses bash-it/bash-it#1632

Alsö, code style cleanup: quote variables, handle unbound parameters,  &c.

plugins/available/less-pretty-cat.plugin.bash

@@ -1,13 +1,9 @@
+# shellcheck shell=bash
 cite about-plugin
 about-plugin 'pygmentize instead of cat to terminal if possible'
 
-if $(command -v pygmentize &> /dev/null) ; then
-  # get the full paths to binaries
-  CAT_BIN=$(which cat)
-  LESS_BIN=$(which less)
-  BASH_IT_CCAT_STYLE="${BASH_IT_CCAT_STYLE:=default}"
-  BASH_IT_CLESS_STYLE="${BASH_IT_CLESS_STYLE:=default}"
-
+if _command_exists pygmentize
+then
   # pigmentize cat and less outputs - call them ccat and cless to avoid that
   # especially cat'ed output in scripts gets mangled with pygemtized meta characters
   function ccat()
@@ -15,17 +11,21 @@ if $(command -v pygmentize &> /dev/null) ; then
       about 'runs either pygmentize or cat on each file passed in'
       param '*: files to concatenate (as normally passed to cat)'
       example 'cat mysite/manage.py dir/text-file.txt'
-      for var;
+		local file
+		: "${BASH_IT_CCAT_STYLE:=default}"
+
+      for file in "$@"
       do
-          pygmentize -f 256 -O style="$BASH_IT_CCAT_STYLE" -g "$var" 2>/dev/null || "$CAT_BIN" "$var";
+          pygmentize -f 256 -O style="$BASH_IT_CCAT_STYLE" -g "$file" 2>/dev/null || command cat "$file";
       done
   }
 
   function cless()
   {
-      about 'it pigments the file passed in and passes it to less for pagination'
+      about 'pigments the file passed in and passes it to less for pagination'
       param '$1: the file to paginate with less'
       example 'less mysite/manage.py'
-      pygmentize -f 256 -O style="$BASH_IT_CLESS_STYLE" -g $* | "$LESS_BIN" -R
+		: "${BASH_IT_CLESS_STYLE:=default}"
+      pygmentize -f 256 -O style="$BASH_IT_CLESS_STYLE" -g "$@" | command less -R
   }
 fi