fix: seemingly redundant checks, these can actually fix errors at times

These checks seem redundant, but in my use, adding them actually removes
a few errors if the function is called repeatedly. This should
*probably* be moved to a function, but I can't think of a name for it,
so for now, I will just leave it here.

lua/tabnine/completion.lua

@@ -13,10 +13,11 @@ local function valid_response(response)
 end
 
 function M.accept()
-	M.clear()
-	if not state.rendered_completion then
+	if not state.completions_cache or not state.rendered_completion then
 		return
 	end
+
+	M.clear()
 	local lines = utils.str_to_lines(state.rendered_completion)
 
 	if utils.starts_with(state.rendered_completion, "\n") then
@@ -34,6 +35,10 @@ function M.accept()
 end
 
 function M.clear()
+	if not state.completions_cache or not state.rendered_completion then
+		return
+	end
+
 	if state.cancel_completion then
 		state.cancel_completion()
 	end