Avoid val() when returning from MSC.execute()

This can be noticed in profiling when passing arrays to iclosures, for example. In a lot of cases the string builder does not need to complete, so a potentially expensive CArray.val() can be avoided.

src/main/java/com/laytonsmith/core/MethodScriptCompiler.java

@@ -3087,10 +3087,13 @@ public static Mixed execute(ParseTree root, Environment env, MethodScriptComplet
 			Mixed retc = script.eval(gg, env);
 			if(root.numberOfChildren() == 1) {
 				returnable = retc;
+				if(done == null) {
+					// string builder is not needed, so return immediately
+					return returnable;
+				}
 			}
-			@SuppressWarnings("null")
-			String ret = retc instanceof CNull ? "null" : retc.val();
-			if(ret != null && !ret.trim().isEmpty()) {
+			String ret = retc.val();
+			if(!ret.trim().isEmpty()) {
 				b.append(ret).append(" ");
 			}
 		}