Extend .tid files to allow single line text fields

To make it easier to create tiddlers that don’t include a terminating
newline in their text

boot/boot.js

@@ -1166,8 +1166,6 @@ $tw.modules.define("$:/boot/tiddlerdeserializer/tid","tiddlerdeserializer",{
 		}
 		if(split.length >= 2) {
 			fields.text = split.slice(1).join("\n\n");
-		} else {
-			fields.text = "";
 		}
 		return [fields];
 	}