fix(frontends/lean/dependencies): compilation warning

Signed-off-by: Leonardo de Moura <leonardo@microsoft.com>

src/frontends/lean/dependencies.cpp

@@ -22,11 +22,11 @@ bool consume_until_import(environment const & env, scanner & s) {
     while (true) {
         try {
             t = s.scan(env);
-        } catch (...) {}
             if (t == scanner::token_kind::Eof)
                 return false;
             if (t == scanner::token_kind::CommandKeyword && s.get_token_info().value() == import)
                 return true;
+        } catch (...) {}
     }
 }