Fix init error in test

Note: due to const-fold, the code does not misbehave at runtime.
However, it's still good to report errors here, as in this case
const-fold changes the semantics of programs, which is too subtle for end users.

The field `elemSeparator` and `caseSeparator` are used before they are initialized.

-- Error: tests/run/typeclass-derivation2a.scala:31:22 -------------------------
31 |    private final val elemSeparator = '\000'
   |                      ^
   |Access non-initialized field value elemSeparator. Calling trace:
   | -> initLabels(0, 0, new mutable.ArrayBuffer[String], new mutable.ArrayBuffer[Array[String]])	[ typeclass-derivation2a.scala:29 ]
   |  -> else if (labelsStr(cur) == elemSeparator)	[ typeclass-derivation2a.scala:43 ]
-- Error: tests/run/typeclass-derivation2a.scala:32:22 -------------------------
32 |    private final val caseSeparator = '\001'
   |                      ^
   |Access non-initialized field value caseSeparator. Calling trace:
   | -> initLabels(0, 0, new mutable.ArrayBuffer[String], new mutable.ArrayBuffer[Array[String]])	[ typeclass-derivation2a.scala:29 ]
   |  -> else if (labelsStr(cur) == caseSeparator)	[ typeclass-derivation2a.scala:41 ]
2 errors found

Author: liufengyun

tests/run/typeclass-derivation2a.scala

@@ -25,12 +25,12 @@ object TypeLevel {
     def mirror(ordinal: Int): Mirror =
       mirror(ordinal, EmptyProduct)
 
-    val label: Array[Array[String]] =
-      initLabels(0, 0, new mutable.ArrayBuffer[String], new mutable.ArrayBuffer[Array[String]])
-
     private final val elemSeparator = '\000'
     private final val caseSeparator = '\001'
 
+    val label: Array[Array[String]] =
+      initLabels(0, 0, new mutable.ArrayBuffer[String], new mutable.ArrayBuffer[Array[String]])
+
     private def initLabels(start: Int, cur: Int,
                            elems: mutable.ArrayBuffer[String],
                            cases: mutable.ArrayBuffer[Array[String]]): Array[Array[String]] = {