[lldb] Avoid resource leak
Summary:
Before the pointer variable `args_dict` was assigned the result of an
allocation with `new` and then `args_dict` is passed to
`GetValueForKeyAsDictionary` which immediatly and unconditionally
assigns `args_dict` to `nullptr`:
```
bool GetValueForKeyAsDictionary(llvm::StringRef key,
Dictionary *&result) const {
result = nullptr;
```
This caused a memory leak which was found in my coverity scan instance
under CID 224753: https://scan.coverity.com/projects/kwk-llvm-project.
Reviewers: jankratochvil, teemperor
Reviewed By: teemperor
Subscribers: teemperor, lldb-commits
Tags: #lldb
Differential Revision: https://reviews.llvm.org/D68638
llvm-svn: 374071