Defer: Pop elements off the defer-stack when returning

We restore the count later, but this fix makes it so that the compiler
doesn't get stuck in an infinite loop when you try to compile the
following code:

```
fn main(): int {
  defer return 5;
  return 1;
}
```

1 files changed, 4 insertions, 2 deletions

diff --git a/src/generator.c b/src/generator.c
index 403bf4a..7de9d32 100644
--- a/src/generator.c
+++ b/src/generator.c
@@ -251,8 +251,10 @@ void generate_statement(Node *stmt, FILE *out)
         fprintf(out, "    push rax\n"); // Save the return value
 
         // Run all the defer statements
-        for (int i = defer_stack_count - 1; i >= 0; i--)
-            generate_statement(defer_stack[i], out);
+        i64 old_count = defer_stack_count;
+        while (defer_stack_count > 0)
+            generate_statement(defer_stack[--defer_stack_count], out);
+        defer_stack_count = old_count;
 
         // TODO: Only do this if we have local variables
         fprintf(out, "    pop rax\n");