core: Fix restoration of loop target in try statement

old_loop_target is only assigned if ctx.loop_target is overwritten,
meaning that if ctx.loop_target is never overwritten, ctx.loop_target
will always be overwritten to None.

We fix this by only restoring from old_loop_target if we previously
assigned to old_loop_target.

nac3core/src/codegen/stmt.rs

@@ -789,10 +789,7 @@ pub fn gen_try<'ctx, 'a, G: CodeGenerator>(
         ctx.outer_catch_clauses = old_clauses;
         ctx.unwind_target = old_unwind;
         ctx.return_target = old_return;
-        if let Some(old_loop_target) = old_loop_target {
-            ctx.loop_target.replace(old_loop_target);
-        }
-        old_loop_target = None;
+        ctx.loop_target = old_loop_target.or(ctx.loop_target).take();
 
         let old_unwind = if !finalbody.is_empty() {
             let final_landingpad = ctx.ctx.append_basic_block(current_fun, "try.catch.final");
@@ -913,9 +910,7 @@ pub fn gen_try<'ctx, 'a, G: CodeGenerator>(
         }
 
         ctx.unwind_target = old_unwind;
-        if let Some(old_loop_target) = old_loop_target {
-            ctx.loop_target.replace(old_loop_target);
-        }
+        ctx.loop_target = old_loop_target.or(ctx.loop_target).take();
         ctx.return_target = old_return;
 
         ctx.builder.position_at_end(landingpad);