Reject a null dictionary in inflateSetDictionary().

[samuelgirmametaferia]

Summary

Reject a null dictionary in inflateSetDictionary() before raw-inflate dictionary handling reaches updatewindow().

The API documentation already specifies that a null dictionary is an invalid parameter and should return Z_STREAM_ERROR. The zlib-wrapper path happens to reject it because the stream is not in DICT, but raw inflate permits dictionaries at any time. In that mode, a nonzero dictLength with dictionary == Z_NULL reaches updatewindow() and passes a null source to the window copy, causing a crash.

deflateSetDictionary() already validates the same pointer. This change makes the inflate side match the documented contract and adds coverage for the raw-inflate case.

Validation

• pristine origin/develop: inflateSetDictionary(&strm, Z_NULL, 1) after inflateInit2(&strm, -15) triggers UBSan and then an ASan null-read in updatewindow()
• patched focused call: returns Z_STREAM_ERROR (-2)
• CMake build: pass
• CTest: 15/15 tests pass, including infcover
• git diff --check: pass