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

This reverts commit eac6a3080d ("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;