Fix a small glitch

Fix a small glitch

When choosing a code language that has dialects in the languages
combo box, the dialects combo gets activated also when minted is
in use. However, minted does not support the concept of dialects
and the combo should not be enabled. This is harmless because the
dialects are simply ignored and the dialects status is restored
after apply, but it may fool the user in thinking that a dialect
can be actually selected. So, always disable it with minted.