Add comment about used exception code

src/IO/VarInt.h

@@ -193,6 +193,9 @@ inline const char * readVarUInt(UInt64 & x, const char * istr, size_t size)
 
 [[noreturn]] inline void throwValueTooLargeForVarIntEncodingException(UInt64 x)
 {
+    /// Under practical circumstances, we should virtually never end up here but AST Fuzzer manages to create superlarge input integers
+    /// which trigger this exception. Intentionally not throwing LOGICAL_ERROR or calling abort() or [ch]assert(false), so AST Fuzzer
+    /// can swallow the exception and continue to run.
     throw Exception(ErrorCodes::BAD_ARGUMENTS, "Value {} is too large for VarInt encoding", x);
 }