src: kwlib: improve command_exists check

Use only the first "word" from a command line to check if the command
exists or not.

Reviewed-by: Rodrigo Siqueira <siqueirajordao@riseup.net>
Signed-off-by: Rubens Gomes Neto <rubens.gomes.neto@usp.br>

src/kwlib.sh

@@ -370,13 +370,12 @@ function store_statistics_data()
 function command_exists()
 {
   local command="$1"
-  #shellcheck disable=SC2206 #FIXME: see issue #388
-  local package=($command)
+  local package=${command%% *}
 
-  if [[ -x "$(command -v "${package[@]}")" ]]; then
-    return 0
+  if [[ ! -x "$(command -v "$package")" ]]; then
+    return 22 # EINVAL
   fi
-  return 22 # EINVAL
+  return 0
 }
 
 # This function exits with a custom error message