bug: cache probe still performed even if count == 0

[johnstcn]

A common practice I've found for the envbuilder_cached_image resource is the following:

resource "envbuilder_cached_image" "cached" {
  count = data.coder_workspace.me.start_count
  ...
}

However, when start_count is 0 I've still observed the resource being re-created.
This results in workspace shutdowns taking longer than they need, especially for large images.