[BOLT][DWARF] Add a nullptr check for DW_AT_call_site to ensure Function will not be empty

[zr33]

Summary

The Function pointer might be NULL and the update process will crash, add a nullptr check to avoid it.

[zr33]

git-clang-format

[ayermolo]

Test?

bolt/lib/Rewrite/DWARFRewriter.cpp

case dwarf::DW_TAG_catch_block: {
                                      AbbrevWriter);
       break;
     }
     case dwarf::DW_TAG_call_site: {
       auto patchPC = [&](AttrInfo &AttrVal, StringRef Entry) -> void {
         Optional<uint64_t> Address = AttrVal.V.getAsAddress();
         const BinaryFunction *Function =
             BC.getBinaryFunctionContainingAddress(*Address);
+        if (!Function)
+          return;
         const uint64_t UpdatedAddress =
             Function->translateInputToOutputAddress(*Address);
         const uint32_t Index =
             AddrWriter->getIndexFromAddress(UpdatedAddress, Unit);
         if (AttrVal.V.getForm() == dwarf::DW_FORM_addrx)
           DebugInfoPatcher.addUDataPatch(AttrVal.Offset, Index, AttrVal.Size);
         else
           errs() << "BOLT-ERROR: unsupported form for " << Entry << "\n";