Add note about pointer state after the call.

[steveklabnik]

Fixes#23422

[rust-highfive]

r? @alexcrichton

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[alexcrichton]

Some reallocations can succeed in-place I believe, so in that sense this may not be 100% true because the same pointer could be returned. Perhaps something like:

The memory at the passed-in pointer is undefined after the call if the allocation was relocated.

[steveklabnik]

@alexcrichton fixed, i just re-ordered the sentence

[alexcrichton]

stray double newline, I'd also tend to preserve the surrounding style by wrapping to 80 chars as well. Other than that though r=me

[steveklabnik]

Our vim files auto-wrap at 100, so doing this is a manual thing, which kinda sucks. I'll still do it here, this just keeps cropping up.

[steveklabnik]

@bors: r=alexcrichton rollup

[bors]

📌 Commit 2750e3c has been approved by alexcrichton