[terminal] IDEA-350567 Edit POWERLEVEL9K_INSTANT_PROMPT only if it is present

IJ-CR-130582

(cherry picked from commit 4d0a0c882d316f7375522c135697fd6f2c51c281)

GitOrigin-RevId: f9136916112a86384ca0cf776e1ac43cc24b249e

plugins/terminal/resources/shell-integrations/zsh/.zshenv

@@ -63,7 +63,7 @@ precmd_functions+=(_jedi_precmd_hook)
 
 # Disable p10k Instant Prompt feature: https://github.com/romkatv/powerlevel10k#instant-prompt
 # because it breaks our command blocks integration by showing the prompt immediately before '.zshrc' is fully sourced
-if [ -n "${INTELLIJ_TERMINAL_COMMAND_BLOCKS:-}" ]
+if [ -n "${POWERLEVEL9K_INSTANT_PROMPT:-}" ] && [ -n "${INTELLIJ_TERMINAL_COMMAND_BLOCKS:-}" ]
 then
   builtin typeset -g POWERLEVEL9K_INSTANT_PROMPT=off
 fi