Allow bundle size to be 0 in clang-offload-bundler

[yaxunl]

Summary

HIP uses clang-offload-bundler to create fat binary. The bundle for host is empty.
Currently clang-offload-bundler checks if the bundle size is 0 when unbundling.
If so it will exit without unbundling the remaining bundles. This causes
clang-offload-bundler not being able to unbundle fat binaries generated for HIP.

This patch allows bundles size to be 0 when clang-offload-bundler unbundles
input files.

[rjmccall]

I really don't understand this well enough to review.

[yaxunl]

Alexey, could you please also review this patch? Thanks.

[ABataev]

LG

tools/clang-offload-bundler/ClangOffloadBundler.cpp

for (uint64_t i = 0; i < NumberOfBundles; ++i) {
       // Read triple.
       if (ReadChars + TripleSize > FC.size())
         return;
 
       StringRef Triple(&FC.data()[ReadChars], TripleSize);
       ReadChars += TripleSize;
 
       // Check if the offset and size make sense.
-      if (!Size || !Offset || Offset + Size > FC.size())
+      if (!Offset || Offset + Size > FC.size())
         return;
 
       assert(BundlesInfo.find(Triple) == BundlesInfo.end() &&
              "Triple is duplicated??");
       BundlesInfo[Triple] = BundleInfo(Size, Offset);
     }
     // Set the iterator to where we will start to read.
     CurBundleInfo = BundlesInfo.begin();