Fix parameter check in RecordBuilder#setSystemChar()

The parameter check did not fail on indix values greater than 2 which
exceeds the space for system chars in Marc 21 records.

Fixes #283

(cherry picked from commit f96ef28)

metafacture-biblio/src/main/java/org/metafacture/biblio/iso2709/RecordBuilder.java

@@ -122,7 +122,7 @@ public void setSystemChars(final char[] systemChars) {
     }
 
     public void setSystemChar(final int index, final char value) {
-        Require.that(0 <= index && index < IMPL_CODES_LENGTH);
+        Require.that(0 <= index && index < SYSTEM_CHARS_LENGTH);
         Require.that(value < Iso646Constants.MAX_CHAR_CODE);
         label.setSystemChar(index, value);
     }

metafacture-biblio/src/test/java/org/metafacture/biblio/iso2709/RecordBuilderTest.java

@@ -183,6 +183,11 @@ public void shouldThrowExceptionIfSystemCharsIsNull() {
         builder.setSystemChars(null);  // Exception expected
     }
 
+    @Test(expected = IllegalArgumentException.class)
+    public void shouldThrowExceptionIfSystemCharIndexGreaterThan2() {
+        builder.setSystemChar(3, '1');
+    }
+
     @Test
     public void shouldWriteReserverdCharToRecordLabel() {
         builder.setReservedChar('R');