[LLDB][NFC] Reliability fixes for ObjectFileMachO.cpp (part 2)

[fixathon]

Summary

Add the fixes suggested post-push in D131554

[fixathon]

Implemented most fixes suggested in https://reviews.llvm.org/D131554 post-push.

lldb/source/Plugins/ObjectFile/Mach-O/ObjectFileMachO.cpp

auto ParseSymbolLambda = [&](struct nlist_64 &nlist, uint32_t nlist_idx,
         }
       } else {
         uint8_t n_type = N_TYPE & nlist.n_type;
         sym[sym_idx].SetExternal((N_EXT & nlist.n_type) != 0);
 
         switch (n_type) {
         case N_INDR: {
           const char *reexport_name_cstr = strtab_data.PeekCStr(nlist.n_value);
-          if (reexport_name_cstr && reexport_name_cstr[0]) {
+          if (reexport_name_cstr && reexport_name_cstr[0] && symbol_name) {
             type = eSymbolTypeReExported;
             ConstString reexport_name(reexport_name_cstr +
                                       ((reexport_name_cstr[0] == '_') ? 1 : 0));
             sym[sym_idx].SetReExportedSymbolName(reexport_name);
             set_value = false;
             reexport_shlib_needs_fixup[sym_idx] = reexport_name;
-            indirect_symbol_names.insert(ConstString(
-                symbol_name +
-                ((symbol_name && (symbol_name[0] == '_')) ? 1 : 0)));
+            indirect_symbol_names.insert(
+                ConstString(symbol_name + ((symbol_name[0] == '_') ? 1 : 0)));
           } else
             type = eSymbolTypeUndefined;
         } break;
 
         case N_UNDF:
           if (symbol_name && symbol_name[0]) {
             ConstString undefined_name(symbol_name +
                                        ((symbol_name[0] == '_') ? 1 : 0));
if (lc.cmd == LC_NOTE) {
         offset = fileoff;
         // Read the struct all_image_infos_header.
         uint32_t version = m_data.GetU32(&offset);
         if (version != 1) {
           return image_infos;
         }
         uint32_t imgcount = m_data.GetU32(&offset);
         uint64_t entries_fileoff = m_data.GetU64(&offset);
-        /* leaving the following dead code as comments for spec documentation
-            offset += 4; // uint32_t entries_size;
-            offset += 4; // uint32_t unused;
-        */
+        // 'entries_size' is not used, nor is the 'unused' entry.
+        //  offset += 4; // uint32_t entries_size;
+        //  offset += 4; // uint32_t unused;
 
         offset = entries_fileoff;
         for (uint32_t i = 0; i < imgcount; i++) {
           // Read the struct image_entry.
           offset_t filepath_offset = m_data.GetU64(&offset);
           uuid_t uuid;
           memcpy(&uuid, m_data.GetData(&offset, sizeof(uuid_t)),
                  sizeof(uuid_t));