[lld-macho] Fix assert when splitting section

[keith]

Summary

Fixes https://github.com/llvm/llvm-project/issues/59649

[int3]

Thanks!

lld/MachO/InputFiles.cpp

if (sec.align >= 32) {
       continue;
     }
     Section &section = *sections.back();
     uint32_t align = 1 << sec.align;
     ArrayRef<uint8_t> data = {isZeroFill(sec.flags) ? nullptr
                                                     : buf + sec.offset,
                               static_cast<size_t>(sec.size)};
 
-    auto splitRecords = [&](int recordSize) -> void {
+    auto splitRecords = [&](size_t recordSize) -> void {
       if (data.empty())
         return;
       Subsections &subsections = section.subsections;
       subsections.reserve(data.size() / recordSize);
       for (uint64_t off = 0; off < data.size(); off += recordSize) {
         auto *isec = make<ConcatInputSection>(
-            section, data.slice(off, recordSize), align);
+            section, data.slice(off, std::min(data.size(), recordSize)), align);
         subsections.push_back({off, isec});
       }
       section.doneSplitting = true;
     };
 
     if (sectionType(sec.flags) == S_CSTRING_LITERALS ||
         (config->dedupLiterals && isWordLiteralSection(sec.flags))) {
       if (sec.nreloc && config->dedupLiterals)