fix: honor explicit nodata value override

[michaelmattig]

Here is a brief summary of what I did:

[coveralls]

Coverage Report for CI Build 31587787786

Coverage increased (+0.001%) to 87.708%

Details

• Coverage increased (+0.001%) from the base build.
• Patch coverage: 4 uncovered changes across 1 file (40 of 44 lines covered, 90.91%).
• No coverage regressions found.

Uncovered Changes

File	Changed	Covered	%
geoengine/operators/src/source/gdal_worker_process/process_impl.rs	44	40	90.91%

Coverage Regressions

No coverage regressions found.

---

Coverage Stats

Relevant Lines:	142697
Covered Lines:	125157
Line Coverage:	87.71%
Coverage Strength:	491169.52 hits per line

---

💛 - Coveralls