added return in guard clause for empty drawcmd buffer

draw(cmd) had a bug causing the first drawcmd in every frame to be added twice, for text this would cause a double free

src/corelib/render.c

@@ -344,6 +344,7 @@ void insert_drawcmd_at(size_t index, const drawcmd_t* cmd) {
 void draw(const drawcmd_t* cmd) {
 	if(g_drawdata_endptr == g_drawdata) {
 		insert_drawcmd_at(0, cmd);
+		return;
 	}
 	long top = (size_t)(g_drawdata_endptr - g_drawdata),
 		 bot = 0,