Various bug fixes (#778)

zencore fixes:
- filesystem.cpp: ReadFile error reporting logic
- compactbinaryvalue.h: CbValue::As*String error reporting logic

zenhttp fixes:
- httpasio BindAcceptor would `return 0;` in a function returning `std::string` (UB)
- httpsys async workpool initialization race

zenstore fixes:
- cas.cpp: GetFileCasResults Results param passed by value instead of reference (large chunk results were silently lost)
- structuredcachestore.cpp: MissCount unconditionally incremented (counted hits as misses)
- cacherpc.cpp: Wrong boolean in Incomplete response array (all entries marked incomplete)
- cachedisklayer.cpp: sizeof(sizeof(...)) in two validation checks computed sizeof(size_t) instead of struct size
- buildstore.cpp: Wrong hash tracked in GC key list (BlobHash pushed twice instead of MetadataHash)
- buildstore.cpp: Removed duplicate m_LastAccessTimeUpdateCount increment in PutBlob

zenserver fixes:
- httpbuildstore.cpp: Reversed subtraction in HTTP range calculation (unsigned underflow)
- hubservice.cpp: Deadlock in Provision() calling Wake() while holding m_Lock (extracted WakeLocked helper)
- zipfs.cpp: Data race in GetFile() lazy initialization (added RwLock with shared/exclusive paths)

1 files changed, 16 insertions, 4 deletions

diff --git a/src/zenserver/frontend/zipfs.cpp b/src/zenserver/frontend/zipfs.cpp
index f9c2bc8ff..42df0520f 100644
--- a/src/zenserver/frontend/zipfs.cpp
+++ b/src/zenserver/frontend/zipfs.cpp
@@ -149,13 +149,25 @@ ZipFs::ZipFs(IoBuffer&& Buffer)
 IoBuffer
 ZipFs::GetFile(const std::string_view& FileName) const
 {
-	FileMap::iterator Iter = m_Files.find(FileName);
-	if (Iter == m_Files.end())
 	{
-		return {};
+		RwLock::SharedLockScope _(m_FilesLock);
+
+		FileMap::const_iterator Iter = m_Files.find(FileName);
+		if (Iter == m_Files.end())
+		{
+			return {};
+		}
+
+		const FileItem& Item = Iter->second;
+		if (Item.GetSize() > 0)
+		{
+			return IoBuffer(IoBuffer::Wrap, Item.GetData(), Item.GetSize());
+		}
 	}
 
-	FileItem& Item = Iter->second;
+	RwLock::ExclusiveLockScope _(m_FilesLock);
+
+	FileItem& Item = m_Files.find(FileName)->second;
 	if (Item.GetSize() > 0)
 	{
 		return IoBuffer(IoBuffer::Wrap, Item.GetData(), Item.GetSize());