Don't ICE if crate has no valid crate types left

[oli-obk]

fixes #50993

[rust-highfive]

r? @eddyb

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[oli-obk]

This is not the source of the regression. Reaching this code is the source of the regression. But it seems a sensible change anyway imo.

If preferred I'll do a bisect and figure out where the real regression happened

[rust-highfive]

The job x86_64-gnu-llvm-3.9 of your PR failed on Travis (raw log). Through arcane magic we have determined that the following fragments from the build log may contain information about the problem.

Click to expand the log.

[00:05:17] travis_fold:start:tidy
travis_time:start:tidy
tidy check
[00:05:17] tidy error: /checkout/src/test/ui/issue-50993.rs: missing trailing newline
[00:05:19] some tidy checks failed
[00:05:19] 
[00:05:19] 
[00:05:19] command did not execute successfully: "/checkout/obj/build/x86_64-unknown-linux-gnu/stage0-tools-bin/tidy" "/checkout/src" "/checkout/obj/build/x86_64-unknown-linux-gnu/stage0/bin/cargo" "--no-vendor" "--quiet"
[00:05:19] 
[00:05:19] 
[00:05:19] failed to run: /checkout/obj/build/bootstrap/debug/bootstrap test src/tools/tidy
[00:05:19] Build completed unsuccessfully in 0:02:10
[00:05:19] Build completed unsuccessfully in 0:02:10
[00:05:19] make: *** [tidy] Error 1
[00:05:19] Makefile:79: recipe for target 'tidy' failed

The command "stamp sh -x -c "$RUN_SCRIPT"" exited with 2.
travis_time:start:33993d5c
$ date && (curl -fs --head https://google.com | grep ^Date: | sed 's/Date: //g' || true)

I'm a bot! I can only do what humans tell me to, so if this was not helpful or you have suggestions for improvements, please ping or otherwise contact @TimNN. (Feature Requests)

[eddyb]

@bors r+

[bors]

📌 Commit 0b1b26f has been approved by eddyb

[bors]

⌛ Testing commit 0b1b26f with merge 67d99d9...

[bors]

☀️ Test successful - status-appveyor, status-travis
Approved by: eddyb
Pushing 67d99d9 to master...