Set SQL editor in Modify Table dialog as read-only programmatically

Otherwise the UI dynamic property does not seem to work, although it
use to and should. Please, improve it if a way to return to the correct
behaviour.

Fixes issue #2078

src/EditTableDialog.cpp

@@ -142,6 +142,8 @@ EditTableDialog::EditTableDialog(DBBrowserDB& db, const sqlb::ObjectIdentifier&
 
     // (De-)activate fields
     checkInput();
+
+    ui->sqlTextEdit->setReadOnly(true);
 }
 
 EditTableDialog::~EditTableDialog()