fix(magic-enter): check for cmd existance before executing

Closes #13294

plugins/magic-enter/magic-enter.plugin.zsh

@@ -10,9 +10,10 @@ magic-enter() {
     return
   fi
 
-  if command jj st >/dev/null 2>&1; then # needs to be before git to handle colocated repositories
+  # needs to be before git to handle colocated repositories
+  if (( $+commands[jj] )) && command jj st >/dev/null 2>&1; then
     BUFFER="$MAGIC_ENTER_JJ_COMMAND"
-  elif command git rev-parse --is-inside-work-tree >/dev/null 2>&1; then
+  elif (( $+commands[git] )) && command git rev-parse --is-inside-work-tree >/dev/null 2>&1; then
     BUFFER="$MAGIC_ENTER_GIT_COMMAND"
   else
     BUFFER="$MAGIC_ENTER_OTHER_COMMAND"