Fix MemoryHistory plugin to check whether the plugin was able to create itself before returning the shared pointer to it. clang warning.
Fix MemoryHistory plugin to check whether the plugin
was able to create itself before returning the shared
pointer to it.
clang warning.


git-svn-id: 4c4cc70b1ef44ba2b7963015e681894188cea27e@219936 91177308-0d34-0410-b5e6-96231b3b80d8

apple/swift-lldb,apple/swift-lldb,llvm-mirror/lldb,apple/swift-lldb,llvm-mirror/lldb,apple/swift-lldb,apple/swift-lldb,apple/swift-lldb,llvm-mirror/lldb,llvm-mirror/lldb,llvm-mirror/lldb