[BUG]: Mojo hangs if you use continue in the nested loop

[zverianskii]

Bug description

Minimum example:

fn main():
    for i in range(4):
        for j in range(4):
            print(i,j)            
        else:
            continue

This pattern is typical if you try to exit nested loop in python:

fn main():
    for i in range(4):
        for j in range(4):
            print(i,j)
            if (i == 2) and (j==2):
                break
        else:
            continue
        break

Steps to reproduce

• Include relevant code snippet or link to code that did not work as expected.
• If applicable, add screenshots to help explain the problem.
• If using the Playground, name the pre-existing notebook that failed and the steps that led to failure.
• Include anything else that might help us debug the issue.

System information

- What OS did you do install Mojo on ? Ubuntu 23
- Provide version information for Mojo by pasting the output of `mojo -v` mojo 0.3.0 (f64f9601)
- Provide Modular CLI version by pasting the output of `modular -v` modular 0.1.4 (6b54d308)

[Mogball]

@weiweichen could you take a look?

[Mogball]

@lispsil Thanks for filing! From a glance, it seems like the behaviour of for ... else is not implemented correctly, causing the else block to always get executed.