InputsOutputs task is not compatible with GitPublishCommit

[grv87]

See ajoberstar/gradle-git-publish#60.

Caused by: java.lang.IllegalStateException: No value has been specified for this provider.
        at org.gradle.api.internal.provider.Providers$1.get(Providers.java:32)
        at org.gradle.api.internal.provider.DefaultPropertyState.get(DefaultPropertyState.java:90)
        at org.gradle.api.internal.provider.DefaultPropertyState.get(DefaultPropertyState.java:90)
        at org.ajoberstar.gradle.git.publish.tasks.GitPublishCommit.getRepoDirectory(GitPublishCommit.java:40)
        at org.ajoberstar.gradle.git.publish.tasks.GitPublishCommit_Decorated.getRepoDirectory(Unknown Source)
        at org.gradle.api.internal.tasks.properties.bean.AbstractNestedRuntimeBeanNode$DefaultPropertyValue$1$1.create(AbstractNestedRuntimeBeanNode.java:83)
        at org.gradle.util.SingleMessageLogger.whileDisabled(SingleMessageLogger.java:313)
        at org.gradle.api.internal.tasks.properties.bean.AbstractNestedRuntimeBeanNode$DefaultPropertyValue$1.get(AbstractNestedRuntimeBeanNode.java:80)
        at com.google.common.base.Suppliers$MemoizingSupplier.get(Suppliers.java:125)
        at org.gradle.api.internal.tasks.properties.bean.AbstractNestedRuntimeBeanNode$DefaultPropertyValue.getValue(AbstractNestedRuntimeBeanNode.java:138)
        at org.gradle.api.internal.tasks.properties.bean.AbstractNestedRuntimeBeanNode$DefaultPropertyValue.call(AbstractNestedRuntimeBeanNode.java:144)
        at org.gradle.api.internal.tasks.DefaultCacheableTaskOutputFilePropertySpec.getOutputFile(DefaultCacheableTaskOutputFilePropertySpec.java:49)
        at org.gradle.api.internal.tasks.properties.GetOutputFilesVisitor.visitOutputFileProperty(GetOutputFilesVisitor.java:44)

        at org.gradle.api.internal.tasks.properties.annotations.AbstractOutputPropertyAnnotationHandler.visitPropertyValue(AbstractOutputPropertyAnnotationHandler.java:35)
        at org.gradle.api.internal.tasks.properties.bean.AbstractNestedRuntimeBeanNode.visitProperties(AbstractNestedRuntimeBeanNode.java:62)
        at org.gradle.api.internal.tasks.properties.bean.RootRuntimeBeanNode.visitNode(RootRuntimeBeanNode.java:32)
        at org.gradle.api.internal.tasks.properties.DefaultPropertyWalker.visitProperties(DefaultPropertyWalker.java:41)
        at org.gradle.api.internal.tasks.TaskPropertyUtils.visitProperties(TaskPropertyUtils.java:39)
        at org.gradle.api.internal.tasks.DefaultTaskOutputs.getFileProperties(DefaultTaskOutputs.java:201)
        at org.gradle.api.internal.tasks.DefaultTaskOutputs$TaskOutputUnionFileCollection.visitContents(DefaultTaskOutputs.java:302)
        at org.gradle.api.internal.file.CompositeFileCollection.getSourceCollections(CompositeFileCollection.java:192)
        at org.gradle.api.internal.file.CompositeFileCollection.iterator(CompositeFileCollection.java:60)
        at org.fidata.gradle.tasks.InputsOutputs$_generate_closure2.doCall(InputsOutputs.groovy:60)
...

This is one instance, but maybe we should expect that other plugins or user's custom tasks could be broken too.

1. We could catch an error for specific task and issue a warning instead
2. Maybe Gradle could do it better when there is an error getting one of files, so that we could still get others.