[analyzer] Provide a check name when MallocChecker enables CStringChecker
[analyzer] Provide a check name when MallocChecker enables CStringChecker

Fix an assertion failure caused by a missing CheckName. The malloc checker
enables "basic" support in the CStringChecker, which causes some CString
bounds checks to be enabled. In this case, make sure that we have a
valid CheckName for the BugType.

git-svn-id: ffe668792ed300d6c2daa1f6eba2e0aa28d7ec6c@323052 91177308-0d34-0410-b5e6-96231b3b80d8

apple/swift-clang,apple/swift-clang,apple/swift-clang,apple/swift-clang,apple/swift-clang,apple/swift-clang,apple/swift-clang,apple/swift-clang,apple/swift-clang,apple/swift-clang