Merge pull request #1690 from dduan/crasher-2-0041

[Sema] add a crasher

Author: gribozavr

validation-test/compiler_crashers_2/0041-walkToDeclPost-crash.swift

@@ -0,0 +1,7 @@
+// RUN: not --crash %target-swift-frontend %s -parse
+
+extension Collection {
+    func f() -> [Generator.Element] {
+        return Array(self.prefix(0))
+    }
+}