[ItaniumDemangle] Fix libcxxabi OutputBuffer::prepend for empty inputs

[slydiman]

See #138564 for details.

[llvmbot]

@llvm/pr-subscribers-libcxxabi

Author: Dmitry Vasilyev (slydiman)

Changes

See #138564 for details.

---

Full diff: https://github.com/llvm/llvm-project/pull/138656.diff

1 Files Affected:

• (modified) libcxxabi/src/demangle/Utility.h (+2)

diff --git a/libcxxabi/src/demangle/Utility.h b/libcxxabi/src/demangle/Utility.h
index 511983ad40f7a..8829f3fa13a93 100644
--- a/libcxxabi/src/demangle/Utility.h
+++ b/libcxxabi/src/demangle/Utility.h
@@ -136,6 +136,8 @@ class OutputBuffer {
 
   OutputBuffer &prepend(std::string_view R) {
     size_t Size = R.size();
+    if (!Size)
+      return *this;
 
     grow(Size);
     std::memmove(Buffer + Size, Buffer, CurrentPosition);