Skip automatic copen when height <= 0

copen and cwindow expect a positive number for the window height so we
can use the value 0 to state that the quickfix window should not be
opened or closed automatically
So when setting g:dispatch_quickfix_height to 0, `:Copen` updates the
quickfix list without opening the quickfix window and prevents the
quickfix window from opening on completion of a `:Dispatch` until the
next explicit `:copen`

Author: shym

autoload/dispatch.vim

@@ -1091,6 +1091,9 @@ endfunction
 function! s:cwindow(request, all, copen) abort
   call s:cgetfile(a:request, a:all)
   let height = get(g:, 'dispatch_quickfix_height', 10)
+  if height <= 0
+    return
+  endif
   let was_qf = s:is_quickfix()
   execute 'botright' (a:copen ? 'copen' : 'cwindow') height
   if !was_qf && s:is_quickfix() && a:copen !=# -2