input/{async,rewind}, decoder/dsdiff: use std::cmp_*() for safer integer comparisons

src/input/AsyncInputStream.cxx

@@ -109,7 +109,7 @@ AsyncInputStream::Seek(std::unique_lock<Mutex> &lock,
 			break;
 
 		const size_t nbytes =
-			new_offset - offset < (offset_type)r.size()
+			std::cmp_less(new_offset - offset, r.size())
 			? new_offset - offset
 			: r.size();
 

src/input/RewindInputStream.cxx

@@ -82,7 +82,7 @@ RewindInputStream::Read(std::unique_lock<Mutex> &lock,
 
 		size_t nbytes = input->Read(lock, ptr, read_size);
 
-		if (input->GetOffset() > (offset_type)sizeof(buffer))
+		if (std::cmp_greater(input->GetOffset(), sizeof(buffer)))
 			/* disable buffering */
 			tail = 0;
 		else if (tail == (size_t)offset) {