[lldb-dap] Fix segfault in JSONUtils.cpp when GetUUIDString() returns nullptr

When creating a stack frame in JSONUtils.cpp CreateStackFrame() the code
constructs a std::string from module.GetUUIDString(), which can return
nullptr in some cases (as documented in the implementation of
SBModule::GetUUIDString()). This causes a segmentation fault when passed to
the std::string constructor.

This fix adds a null check before constructing the UUID string, falling back
to an empty string if nullptr is returned. The existing empty check ensures
the moduleId field is omitted from the JSON when no UUID exists.

Author: aahrun

lldb/tools/lldb-dap/JSONUtils.cpp

@@ -554,7 +554,8 @@ llvm::json::Value CreateStackFrame(DAP &dap, lldb::SBFrame &frame,
 
   lldb::SBModule module = frame.GetModule();
   if (module.IsValid()) {
-    std::string uuid = module.GetUUIDString();
+    const char *uuid_cstr = module.GetUUIDString();
+    std::string uuid = uuid_cstr ? uuid_cstr : "";
     if (!uuid.empty())
       object.try_emplace("moduleId", uuid);
   }