Avoid crash in InitializeNonZerothFrame if no module found

After r221575 TestCallStopAndContinue and TestCallThatRestarts started
crashing on FreeBSD with a null temporary_module_sp in
RegisterContextLLDB::InitializeNonZerothFrame().


git-svn-id: https://llvm.org/svn/llvm-project/lldb/trunk@221805 91177308-0d34-0410-b5e6-96231b3b80d8