Do not reset the stack variables when (re)sourcing the plugin

This is meant to keep the current state when re-sourcing the shell
config (`. ~/.zshrc`).

Closes https://github.com/Tarrasch/zsh-autoenv/pull/24

tests/ZDOTDIR/.zshenv

@@ -2,7 +2,6 @@ test -f "$TESTDIR/.zcompdump" && rm "$TESTDIR/.zcompdump"
 
 AUTOENV_DEBUG=0
 
-source "$TESTDIR/../autoenv.plugin.zsh"
 export AUTOENV_ENV_FILENAME="$PWD/.env_auth"
 
 echo -n > $AUTOENV_ENV_FILENAME

tests/autoenv.t

@@ -74,6 +74,7 @@ Now, will it take no for an answer?
 
 Lets also try one more time to ensure it didn't add it.
 
+  $ _autoenv_ask_for_yes() { echo "yes"; return 0 }
   $ cd .
   Attempting to load unauthorized env file!
   -* /tmp/cramtests-*/autoenv.t/.env (glob)
@@ -84,4 +85,11 @@ Lets also try one more time to ensure it didn't add it.
   
   **********************************************
   
-  Would you like to authorize it? (type 'yes') no
+  Would you like to authorize it? (type 'yes') yes
+  ENTERED
+
+Reloading the script should keep the current state, e.g. when reloading your
+~/.zshrc.
+
+  $ source $TEST_AUTOENV_PLUGIN_FILE
+  $ cd .

tests/setup.sh

@@ -18,6 +18,9 @@ fi
 _save_errexit=${options[errexit]}
 set -e
 
+TEST_AUTOENV_PLUGIN_FILE="$TESTDIR/../autoenv.plugin.zsh"
+source $TEST_AUTOENV_PLUGIN_FILE
+
 # Reset any authentication.
 echo -n >| $AUTOENV_ENV_FILENAME