make realloc with a size of zero fail

[RalfJung]

Fixes https://github.com/rust-lang/miri/issues/2774

[RalfJung]

@bors r+

[bors]

:pushpin: Commit a41b75a89f536cdac70131ee7ce24b3cb1973ffc has been approved by RalfJung

It is now in the queue for this repository.

[bors]

:hourglass: Testing commit a41b75a89f536cdac70131ee7ce24b3cb1973ffc with merge 6274f8ae4b91decabe3c9c0f23b41ad12882f21e...

[bors]

:broken_heart: Test failed - checks-actions

[RalfJung]

@bors r+

[bors]

:pushpin: Commit ab307375b4183cc7fb71db8d18adcbf06e95a82f has been approved by RalfJung

It is now in the queue for this repository.

[bors]

:lock: Merge conflict

This pull request and the master branch diverged in a way that cannot be automatically merged. Please rebase on top of the latest master branch, and let the reviewer approve again.

How do I rebase?

Assuming `self` is your fork and `upstream` is this repository, you can resolve the conflict following these steps: 1. `git checkout realloc` *(switch to your branch)* 2. `git fetch upstream master` *(retrieve the latest master)* 3. `git rebase upstream/master -p` *(rebase on top of it)* 4. Follow the on-screen instruction to resolve conflicts (check `git status` if you got lost). 5. `git push self realloc --force-with-lease` *(update this PR)* You may also read [*Git Rebasing to Resolve Conflicts* by Drew Blessing](http://blessing.io/git/git-rebase/open-source/2015/08/23/git-rebasing-to-resolve-conflicts.html) for a short tutorial. Please avoid the ["**Resolve conflicts**" button](https://help.github.com/articles/resolving-a-merge-conflict-on-github/) on GitHub. It uses `git merge` instead of `git rebase` which makes the PR commit history more difficult to read. Sometimes step 4 will complete without asking for resolution. This is usually due to difference between how `Cargo.lock` conflict is handled during merge and rebase. This is normal, and you should still perform step 5 to update this PR.

Error message

```text Auto-merging src/shims/foreign_items.rs CONFLICT (content): Merge conflict in src/shims/foreign_items.rs Automatic merge failed; fix conflicts and then commit the result. ```

[RalfJung]

@bors r+

[bors]

:pushpin: Commit c2562d01382ee69094f9706ebd6d3f0cc1cd9484 has been approved by RalfJung

It is now in the queue for this repository.

[bors]

:hourglass: Testing commit c2562d01382ee69094f9706ebd6d3f0cc1cd9484 with merge 5dfccc2b9fef5ca5d3d88315842811f7b14865f7...

[bors]

:sunny: Test successful - checks-actions Approved by: RalfJung Pushing 5dfccc2b9fef5ca5d3d88315842811f7b14865f7 to master...