refactor: Avoid sign-compare compiler warning in util/asmap

This reverts commit eac6a30 ("refactor:
Rework asmap Interpret to avoid ptrdiff_t"), because it is UB to form a
past-the-end iterator, even if it is never dereferenced.

Then fix the compiler warning in a different way:
Instead of comparing an uint32_t against a signed ptrdiff_t, just
promote both to a type that can represent both types.

Even though in this case the ptrdiff_t should never hold a negative
value, the overhead from promotion should be negligible.

src/util/asmap.cpp

@@ -93,8 +93,7 @@ uint32_t Interpret(const std::vector<bool> &asmap, const std::vector<bool> &ip)
  jump = DecodeJump(pos, endpos);
  if (jump == INVALID) break; // Jump offset straddles EOF
  if (bits == 0) break; // No input bits left
- if (pos + jump < pos) break; // overflow
- if (pos + jump >= endpos) break; // Jumping past EOF
+ if (int64_t{jump} >= int64_t{endpos - pos}) break; // Jumping past EOF
  if (ip[ip.size() - bits]) {
  pos += jump;
  }
@@ -156,8 +155,7 @@ bool SanityCheckASMap(const std::vector<bool>& asmap, int bits)
  } else if (opcode == Instruction::JUMP) {
  uint32_t jump = DecodeJump(pos, endpos);
  if (jump == INVALID) return false; // Jump offset straddles EOF
- if (pos + jump < pos) return false; // overflow
- if (pos + jump > endpos) return false; // Jump out of range
+ if (int64_t{jump} > int64_t{endpos - pos}) return false; // Jump out of range
  if (bits == 0) return false; // Consuming bits past the end of the input
  --bits;
  uint32_t jump_offset = pos - begin + jump;