Fix matching zero-length strings.

Author: Moderocky

src/main/java/org/byteskript/skript/lang/syntax/literal/StringLiteral.java

@@ -79,6 +79,7 @@ else if (escape) {
 
     @Override
     public Pattern.Match match(String thing, Context context) {
+        if (thing.length() < 2) return null;
         if (thing.charAt(0) != '"') return null;
         if (thing.charAt(thing.length() - 1) != '"') return null;
         final String contents = thing.substring(1, thing.length() - 1);

src/test/resources/maths.bsk

@@ -21,4 +21,5 @@ function basic:
         assert {d} is 4: "Multiplication failed."
         assert {e} is 2: "Square root (syntax) failed."
         assert "hello " + "there" is "hello there": "String joining failed."
+        assert "Hello " + "<there!" is "Hello <there!": "String joining failed."