Fix missing value for first item of enums with trailing comma

The value of the first item of an enum with a trailing comma after its
last item was not correctly initialized to 0 any more after the changes
of 74adaa5738 (see #1515) because "_last"
attribute was not set correctly in this case.

Do set it for the last item when it's followed by a comma too and add
more unit tests checking for this.

Closes #1566.

Examples/test-suite/java_enums.i

@@ -18,6 +18,21 @@ import java.io.*; // For Serializable
 // Set default Java const code generation
 %javaconst(1);
 
+// Test enums with trailing comma after the last item.
+enum WithTrailingComma
+{
+    First,
+    Second,
+};
+
+%ignore ReallyFirstOneIsIgnored;
+enum WithTrailingCommaAndIgnoredFirstItem
+{
+    ReallyFirstOneIsIgnored,
+    FirstNonIgnoredOne,
+    SecondNonIgnoredOne,
+};
+
 // Change the default generation so that these enums are generated into an interface instead of a class
 %typemap(javaclassmodifiers) enum stuff "public interface"