fix(exposure): convert colorspace on all read paths and guard EV metadata

Address review feedback:
- fileIO loadImage: move colorconvert out of the branch chain so the missing
  and invalid EVComp paths also return the image in the requested colorspace,
  instead of leaking a LINEAR image to the cache.
- main_prepareDenseScene: guard the EV computation as well, so a missing-exposure
  -1 sentinel no longer writes NaN (log2 of a negative) into AliceVision:EV.

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

Author: Your Name

src/aliceVision/mvsUtils/fileIO.cpp

@@ -438,9 +438,9 @@ void loadImage(const std::string& path, const MultiViewParams& mp, int camId, Im
                 img(i)[1] *= exposureCompensation;
                 img(i)[2] *= exposureCompensation;
             }
-
-            imageAlgo::colorconvert(img, image::EImageColorSpace::LINEAR, colorspace);
         }
+
+        imageAlgo::colorconvert(img, image::EImageColorSpace::LINEAR, colorspace);
     }
 
     // scale chosen by the user and apply during the process

src/software/pipeline/main_prepareDenseScene.cpp

@@ -244,9 +244,9 @@ bool prepareDenseScene(const SfMData& sfmData,
 
             // add exposure values to images metadata
             const double cameraExposure = view->getImage().getCameraExposureSetting().getExposure();
-            const double ev = std::log2(1.0 / cameraExposure);
-            // only a strictly positive median and camera exposure give a meaningful factor; otherwise getExposure()
-            // returned the -1 sentinel (missing metadata) and dividing would write a degenerate (-inf) EVComp
+            // getExposure() returns the -1 sentinel when metadata is missing; guard both derived values so we never
+            // write a degenerate EV (log2 of a negative -> NaN) or EVComp (division -> -inf) into the image metadata
+            const double ev = (cameraExposure > 0.0) ? std::log2(1.0 / cameraExposure) : 0.0;
             const float exposureCompensation =
                 (medianCameraExposure > 0.0 && cameraExposure > 0.0) ? float(medianCameraExposure / cameraExposure) : 1.0f;
             metadata.push_back(oiio::ParamValue("AliceVision:EV", float(ev)));