message: Check for a null SymbolFile before dereferencing.
  The SymbolVendor proxies were checking for null SymbolFile before
  doing anything with them. We lost that check in
  BreakpointResolverFileLine::SearchCallback, this commit just
  reintroduces it.
diff: @@ -229,8 +229,9 @@ BreakpointResolverFileLine::SearchCallback(SearchFilter &filter,
  search_file_spec.GetDirectory().Clear();
  const size_t num_comp_units = context.module_sp->GetNumCompileUnits();
  - const bool force_check_inlines =
  - context.module_sp->GetSymbolFile()->ForceInlineSourceFileCheck();
  + bool force_check_inlines = false;
  + if (auto *sym_file = context.module_sp->GetSymbolFile())
  + force_check_inlines = sym_file->ForceInlineSourceFileCheck();
  for (size_t i = 0; i < num_comp_units; i++) {
  CompUnitSP cu_sp(context.module_sp->GetCompileUnitAtIndex(i));
  if (cu_sp) {
  