Compiler emits return instructions

Another failure on my part to write the compiler correctly. oops

Signed-off-by: Alek Ratzloff <alekratz@gmail.com>

src/compiler.rs

@@ -701,6 +701,7 @@ impl StmtVisitor for Compiler<'_> {
             let nil = self.insert_constant(self.create_nil())?;
             self.emit(stmt_line_number(stmt), Op::PushConstant(nil));
         }
+        self.emit(stmt_line_number(stmt), Op::Return);
         Ok(())
     }
     fn visit_if_stmt(&mut self, stmt: &IfStmt) -> Result<()> {