opt: mdx -> avoid duplicated Adler-32 checksum in zlib decompression

[shenlebantongying]

close https://github.com/xiaoyifang/goldendict-ng/issues/1775

Micro optimization, remove one extra data traversing.

Adler-32 is a rolling hash calculated together with the inflating process.

Fix various small issues

• move using out of the header (it propagates into all headers that include it)
• create buf only when it will be used (inflateInit == Z_OK)
• check inflateEnd's return value

[sonarcloud[bot]]

Quality Gate passed

Issues
1 New issue
0 Accepted issues

Measures
0 Security Hotspots
0.0% Coverage on New Code
0.0% Duplication on New Code

See analysis details on SonarCloud