fix mangled prompts. closes #30

1. error message printed when no configured upstream branch
2. 256 color code used in precmd doesn't work on my terminal
3. preexec hook mangles output when the command itself contains escape sequences
4. cursor position isn't restored correctly when you have already began typing something before the async command executes

pure.zsh

@@ -38,7 +38,9 @@ prompt_pure_preexec() {
 	cmd_timestamp=$(date +%s)
 
 	# shows the current dir and executed command in the title when a process is active
-	printf "\e]0;$PWD:t: $2\a"
+	print -Pn "\e]0;"
+	echo -nE "$PWD:t: $2"
+	print -Pn "\a"
 }
 
 # string length ignoring ansi escapes
@@ -62,9 +64,11 @@ prompt_pure_precmd() {
 		command git rev-parse --is-inside-work-tree &>/dev/null &&
 		# check check if there is anything to pull
 		command git fetch &>/dev/null &&
+		# check if there is an upstream configured for this branch
+		command git rev-parse --abbrev-ref @'{u}' &>/dev/null &&
 		(( $(command git rev-list --count HEAD...@'{u}' 2>/dev/null) > 0 )) &&
 		# some crazy ansi magic to inject the symbol into the previous line
-		printf "\e[A\e[`prompt_pure_string_length $prompt_pure_preprompt`C\e[90m⇣\e[0m\n\e[2C"
+		print -Pn "\e[s\e[A\e[1G\e[`prompt_pure_string_length $prompt_pure_preprompt`C%F{cyan}⇣%f\e[u"
 	} &!
 
 	# reset value since `preexec` isn't always triggered