[LLD] [COFF] Fix a ubsan error in pdb-type-server-missing.yaml

[mstorsjo]

Summary

This error has been present since rG5519e4da83d1abc66620334692394749eceb0e50.

[rnk]

lgtm

lld/COFF/DebugTypes.cpp

void TypeMerger::mergeTypesWithGHash() {
   std::vector<GHashCell> entries;
   for (const GHashCell &cell :
        makeArrayRef(ghashState.table.table, tableSize)) {
     if (!cell.isEmpty())
       entries.push_back(cell);
   }
   parallelSort(entries, std::less<GHashCell>());
   log(formatv("ghash table load factor: {0:p} (size {1} / capacity {2})\n",
-              double(entries.size()) / tableSize, entries.size(), tableSize));
+              tableSize ? double(entries.size()) / tableSize : 0,
+              entries.size(), tableSize));
 
   // Find out how many type and item indices there are.
   auto mid =
       std::lower_bound(entries.begin(), entries.end(), GHashCell(true, 0, 0));
   assert((mid == entries.end() || mid->isItem()) &&
          (mid == entries.begin() || !std::prev(mid)->isItem()) &&
          "midpoint is not midpoint");
   uint32_t numTypes = std::distance(entries.begin(), mid);