Check if TaskWarrior is present

dotfiles/bash/post.bashrc

@@ -29,6 +29,7 @@ __bashum__save_rv() {
 
 __bashum__task_context() {
     local ctx       # TaskWarrior context
+    type -t task >/dev/null || return 1
     ctx=$(task _get rc.context)
     test -n "$ctx" || return
     echo -n "|$ctx"