fix(imageProcessing): fix guard placement for bilateralFilter and nlmFilter OpenCV checks

The `#if ALICEVISION_HAVE_OPENCV` guards were incorrectly placed
*before* the
`if (pParams.*.enabled)` runtime checks, causing the entire block
(including
the enabled-check) to be silently skipped at compile time when OpenCV is
absent.

- Move the preprocessor guard *inside* the runtime `if` block for
  bilateralFilter
  and nlmFilter, so the enabled-check is always compiled and evaluated
- Add an `#else` branch for nlmFilter that logs an explicit error when
  OpenCV
  is unavailable and the filter is requested, instead of silently bypassing it

Author: Sylvain Maziere

src/software/utils/main_imageProcessing.cpp

@@ -522,7 +522,6 @@ void setupSteps(std::list<std::unique_ptr<ImageProcess>> & steps, const Processi
     {
         steps.push_back(std::make_unique<SharpenProcess>(pParams.sharpen.width, pParams.sharpen.contrast, pParams.sharpen.threshold));
     }
-#if ALICEVISION_IS_DEFINED(ALICEVISION_HAVE_OPENCV)
     if (pParams.bilateralFilter.enabled)
     {
 #if ALICEVISION_IS_DEFINED(ALICEVISION_HAVE_OPENCV)
@@ -547,11 +546,13 @@ void setupSteps(std::list<std::unique_ptr<ImageProcess>> & steps, const Processi
     {
         steps.push_back(std::make_unique<NoiseProcess>(ENoiseMethod_enumToString(pParams.noise.method), pParams.noise.A, pParams.noise.B, pParams.noise.mono));
     }
-#if ALICEVISION_IS_DEFINED(ALICEVISION_HAVE_OPENCV)
     if (pParams.nlmFilter.enabled)
+#if ALICEVISION_IS_DEFINED(ALICEVISION_HAVE_OPENCV)
     {
         steps.push_back(std::make_unique<NlmFilterProcess>(pParams.nlmFilter.filterStrength, pParams.nlmFilter.filterStrengthColor, pParams.nlmFilter.templateWindowSize, pParams.nlmFilter.searchWindowSize));
     }
+#else
+        ALICEVISION_LOG_ERROR("OpenCV support is not enabled in this AliceVision build. Nlm filter processing is unavailable and will be bypassed.");
 #endif
     if (pParams.applyDcpMetadata || pParams.enableColorTempProcessing)
     {