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, 4 insertions, 0 deletions

diff --git a/src/zencore/string.cpp b/src/zencore/string.cpp
index 0ee863b74..a9aed6309 100644
--- a/src/zencore/string.cpp
+++ b/src/zencore/string.cpp
@@ -24,6 +24,10 @@ utf16to8_impl(u16bit_iterator StartIt, u16bit_iterator EndIt, ::zen::StringBuild
 		// Take care of surrogate pairs first
 		if (utf8::internal::is_lead_surrogate(cp))
 		{
+			if (StartIt == EndIt)
+			{
+				break;
+			}
 			uint32_t trail_surrogate = utf8::internal::mask16(*StartIt++);
 			cp						 = (cp << 10) + trail_surrogate + utf8::internal::SURROGATE_OFFSET;
 		}