Auto merge of #2971 - jtgeibel:fix-prerelease-only, r=Turbo87
Auto merge of #2971 - jtgeibel:fix-prerelease-only, r=Turbo87

Fix version logic when there are only pre-releases

It looks like fixing the bug in #2894 exposed this bug. When there are
only pre-release versions of a crate, the version number needs to be
extracted so that the version object can be located again a few lines
later. This could probably be refactored, but for now this removes the
spurious error notification shown in the UI.

r? `@Turbo87`

rust-lang/crates.io,rust-lang/crates.io,rust-lang/crates.io,rust-lang/crates.io