Tolerate bad query result with bzlmod support

[tgeng]

We are seeing the following errors with my previous change 😅 . Apparently bazel query can sometimes fail and as a result bazel-diff crashes due to NPE in such cases. Unfortunately I can't figured out another way to reliably get the path under <bazel-cache/external/ without bazel query so this PR will just fallback to the old bazel external module path if bazel query failed.

09:01:24 GMT-07:00  com.google.common.util.concurrent.UncheckedExecutionException: java.lang.NullPointerException: readLine(...) must not be null
09:01:24 GMT-07:00  	at com.google.common.cache.LocalCache$Segment.get(LocalCache.java:2055)
09:01:24 GMT-07:00  	at com.google.common.cache.LocalCache.get(LocalCache.java:3966)
09:01:24 GMT-07:00  	at com.google.common.cache.LocalCache.getOrLoad(LocalCache.java:3989)
09:01:24 GMT-07:00  	at com.google.common.cache.LocalCache$LocalLoadingCache.get(LocalCache.java:4950)
09:01:24 GMT-07:00  	at com.bazel_diff.hash.ExternalRepoResolver.resolveExternalRepoRoot(ExternalRepoResolver.kt:28)
09:01:24 GMT-07:00  	at com.bazel_diff.hash.SourceFileHasher$digest$1.invoke(SourceFileHasher.kt:58)
09:01:24 GMT-07:00  	at com.bazel_diff.hash.SourceFileHasher$digest$1.invoke(SourceFileHasher.kt:42)
09:01:24 GMT-07:00  	at com.bazel_diff.hash.HashingExtensionsKt.sha256(HashingExtensions.kt:14)
09:01:24 GMT-07:00  	at com.bazel_diff.hash.SourceFileHasher.digest(SourceFileHasher.kt:42)
09:01:24 GMT-07:00  	at com.bazel_diff.hash.BuildGraphHasher$hashSourcefiles$result$1.apply(BuildGraphHasher.kt:71)
09:01:24 GMT-07:00  	at com.bazel_diff.hash.BuildGraphHasher$hashSourcefiles$result$1.apply(BuildGraphHasher.kt:62)
09:01:24 GMT-07:00  	at java.base/java.util.stream.ReferencePipeline$3$1.accept(ReferencePipeline.java:197)
09:01:24 GMT-07:00  	at java.base/java.util.ArrayList$ArrayListSpliterator.forEachRemaining(ArrayList.java:1625)
09:01:24 GMT-07:00  	at java.base/java.util.stream.AbstractPipeline.copyInto(AbstractPipeline.java:509)
09:01:24 GMT-07:00  	at java.base/java.util.stream.ForEachOps$ForEachTask.compute(ForEachOps.java:290)
09:01:24 GMT-07:00  	at java.base/java.util.concurrent.CountedCompleter.exec(CountedCompleter.java:754)
09:01:24 GMT-07:00  	at java.base/java.util.concurrent.ForkJoinTask.doExec(ForkJoinTask.java:373)
09:01:24 GMT-07:00  	at java.base/java.util.concurrent.ForkJoinPool$WorkQueue.topLevelExec(ForkJoinPool.java:1182)
09:01:24 GMT-07:00  	at java.base/java.util.concurrent.ForkJoinPool.scan(ForkJoinPool.java:1655)
09:01:24 GMT-07:00  	at java.base/java.util.concurrent.ForkJoinPool.runWorker(ForkJoinPool.java:1622)
09:01:24 GMT-07:00  	at java.base/java.util.concurrent.ForkJoinWorkerThread.run(ForkJoinWorkerThread.java:165)
09:01:24 GMT-07:00  Caused by: java.lang.NullPointerException: readLine(...) must not be null
09:01:24 GMT-07:00  	at com.bazel_diff.hash.ExternalRepoResolver.runProcessAndCaptureFirstLine(ExternalRepoResolver.kt:44)
09:01:24 GMT-07:00  	at com.bazel_diff.hash.ExternalRepoResolver.resolveBzlModPath(ExternalRepoResolver.kt:33)
09:01:24 GMT-07:00  	at com.bazel_diff.hash.ExternalRepoResolver.access$resolveBzlModPath(ExternalRepoResolver.kt:10)
09:01:24 GMT-07:00  	at com.bazel_diff.hash.ExternalRepoResolver$cache$1.apply(ExternalRepoResolver.kt:24)
09:01:24 GMT-07:00  	at com.bazel_diff.hash.ExternalRepoResolver$cache$1.apply(ExternalRepoResolver.kt:19)
09:01:24 GMT-07:00  	at com.google.common.cache.CacheLoader$FunctionToCacheLoader.load(CacheLoader.java:169)
09:01:24 GMT-07:00  	at com.google.common.cache.LocalCache$LoadingValueReference.loadFuture(LocalCache.java:3533)
09:01:24 GMT-07:00  	at com.google.common.cache.LocalCache$Segment.loadSync(LocalCache.java:2282)
09:01:24 GMT-07:00  	at com.google.common.cache.LocalCache$Segment.lockedGetOrLoad(LocalCache.java:2159)
09:01:24 GMT-07:00  	at com.google.common.cache.LocalCache$Segment.get(LocalCache.java:2049)
09:01:24 GMT-07:00  	... 20 more

[tinder-maxwellelliott]

Thanks