fix(exposure): guard the Median EV log line against the missing-metadata sentinel

Complements the per-image EV guard: when no view has exposure metadata the
median exposure is the -1 sentinel, so log2(1/median) printed -nan(ind) in the
"Median EV" info line. Guard it the same way with a 0.0 fallback. Log-only.

Co-Authored-By: Claude Opus 4.8 <noreply@anthropic.com>

Author: Your Name

src/software/pipeline/main_prepareDenseScene.cpp

@@ -130,7 +130,9 @@ bool prepareDenseScene(const SfMData& sfmData,
 
     // for exposure correction
     const double medianCameraExposure = sfmData.getMedianCameraExposureSetting().getExposure();
-    ALICEVISION_LOG_INFO("Median Camera Exposure: " << medianCameraExposure << ", Median EV: " << std::log2(1.0 / medianCameraExposure));
+    // guard the log2 as above: a missing-metadata median (-1 sentinel) would otherwise print a NaN Median EV
+    const double medianEV = (medianCameraExposure > 0.0) ? std::log2(1.0 / medianCameraExposure) : 0.0;
+    ALICEVISION_LOG_INFO("Median Camera Exposure: " << medianCameraExposure << ", Median EV: " << medianEV);
 
 #pragma omp parallel for num_threads(3)
     for (int i = 0; i < viewIds.size(); ++i)